Category / equine genetics

by Equus ferus Wild Horse Photography

Genetics Part 1: Basic Horse Colour

Part 1: Basic Horse Colour

The first gene we look at is the E or Extention gene. Simply put, it determines RED or BLACK. A horse with two EE or Ee appears black, and ee appears red (chestnut). True black is a fairly uncommon horse coat colour, so where are all the black horses? To answer that, we need the Agouti gene.

EE
eEeEe
eEeEe
Extension gene

The Agouti gene A, determines how much black appears on the coat. This gene ONLY acts on black, so chestnut horses are unaffected.
AA: Black is restricted to the points (legs, mane, and tail) Bay
Aa: Black is restricted to the points (legs, mane, and tail) Bay
aa: Black all over (Black)

AA
aAaAa
aAaAa
GenotypePhenotype
EEAA
EeAA
EEAa
EeAa
EEaa
Eeaa
eeAA
eeAa
eeaa

There is one more gene at the Agouti locus (Locus refers to where on a chromosome the gene is found). It is the At or Seal brown, and this third allele has been recognised to explain the colour Seal Brown – a black horse with red/tan muzzle, flank folds, chest, underarms, and inner ears, which is also referred to as ‘Black & Tan’ due to similarities in colour in canines & rabbits (Doberman, Gordon setter, Rottweiler, French bulldog)

AA: Black is restricted to the points (legs, mane, and tail- Bay)- most dominant
Aa: Black is restricted to the points (legs, mane, and tail- Bay)
AtAt: Black is somewhat restricted (Seal Brown)
Ata: Black is somewhat restricted (Seal Brown)
aa: Black all over (Black)- least dominant

GenotypePhenotype
AA/AAt/aa
(Bay)
AtAt
(Dark Seal Brown: appears darker than Ata)
Ata
(Lighter Seal Brown: appears lighter)
aa
(Black)
At Seal Brown

Some more Seal Brown examples.


Brave from Sand Wash Basin may be a Seal Brown with a more reddish tone or a Bay with an exceptional amount of the Sooty Factor (For a brief review of the sooty factor, go here). The foal shows light areas in the typical locations for Seal Brown (see list below).
Areas with tan/red colour:

  • Muzzle- sides, chin, & top. (the very end of the muzzle is usually dark grey)
  • Beneath the eyes
  • Flank folds (where the hind legs meet the abdomen)
  • Underarms
  • Chest
  • Underbelly
  • Front of Stifle (the area just behind the flank fold on the hind leg, ‘knee’)
  • Quarters (back of thighs)
  • Base of ears
  • Ear tips

The first photo is by the talented Kathy Simpson of Rabbitbrush Photography. Used with permission from SWAT: Sand Wash Wild Horse Advocacy Team. The second photo is by Equusferus and Brave clearly demonstrates the lighter “soft areas” (muzzle, beneath the eyes, flank folds, chest, underarms, underbelly, front of the stifle, quarters (backs of the thighs), and inner ears).

by Equus ferus Wild Horse Photography

Review: Genetics of Equine Color

Part 1: Review of Inheritance

Presenting a brief review of inheritance. In humans, brown eyes are dominant over blue (except in rare circumstances). We’ll use them as our example. Traits are usually represented by letters. Uppercase is dominant, and lowercase is recessive. Brown eyes =BB, and blue eyes = bb. You have two because you inherit one from each parent. For the biology review, we’ll keep it simple, although eye colour is more complex in reality. Two same letters, BB or bb, indicate the person inherited two of the same gene for eye colour from each parent. This is referred to as homozygous (meaning the same).

BB
bBbBb
bBbBb
Dominant Inheritance
BB
bBbBb
bBbBb

Say one parent gives a B and a recessive or lowercase b. The parent has brown eyes but has a hidden recessive b (Bb). This is because B is dominant and overrides the recessive gene b, and the eyes appear brown. If a parent is Bb and they have children with a blue-eyed parent, 50% of the children may have brown eyes, and 50% may have blue. The parents with one dominant and one recessive gene are called heterozygous or “split” for the trait Bb.

Bb
bBbbb
bBbbb
Dominant inheritance
Bb
bBbbb
bBbbb

INCOMPLETE DOMINANCE

“Incomplete Dominance” is where the combination of traits from each parent results in an intermediate colour. In the case of carnations, breeding white and red carnations result in pink flowers; the traits are blended.

CrCr
CwCrCwCrCw
CwCrCwCrCw
Incomplete dominance

If we take the flowers from above, all pink, and breed them together (second generation), we find the genes align the same way as the parents. CrCr= red, CwCw= white, and CwCr =pink.

CrCw
CrCrCrCrCw
CwCrCwCwCw
Incomplete dominance

CODOMINANCE

Some carnations exhibit “Codominance where the trait from each parent is observed without blending, so instead of pink, the flower appears red and white.


by Equus ferus Wild Horse Photography

The Bays & Basic Equine Color Genetics


“ I do not need to tell you to curry the Godolphin Arabian,” he smiled with his eyes. “Already his coat is the color of honey when held in a jar against the sunlight.”

Marguerite Henry’s description of Sham, the Godolphin Arabian, stayed in my mind from the moment I read the book ‘King of the Wind’ as a little girl. Bay horses: a combination of fiery red, and coal-black have captured the imagination of people for millennia.

Heber Bay Stallion, Apache and Sitgreaves National Forests, Arizona
(PLEASE TAP/CLICK ON THE PHOTOGRAPHS TO VIEW A LARGER VERSION)

Colour in animals serves many useful purposes such as ‘concealment, communication, and regulation of physiological process’ (Corbin, et al, 2020). Horses were domesticated approximately 5,500 years ago and selective breeding resulted in the vast array of horse types and colours we see today.

All horses receive two alleles from each parent that determine the base colour. An Allele is each contribution by parents- denoted as EE (each parent contributed one E), or Ee (one parent contributed E, the other parent contributed e). These alleles are located at specific locations on a chromosome called a loci/locus.

Base colours are red or black. The horse begins with the MC1R, or Melanocortin 1 Receptor locus. This determines black or red and is designated by E.

EE Black
Ee: Black
ee: Red

Bay Mare, Salt River, Arizona

Next, the locus that contributes to colour is called the ASIP or Agouti Signaling Protein which determines where the black will appear, either all over, restricted to parts of the body, or only the points (lower legs, mane, tail, tips of ears). There are several subtypes (A, At, A+).

In order to control black, the horse must have at least one E gene (EE, Ee), otherwise, the ASIP has no effect, so no black appears with ‘ee’ and the horse is chestnut.

AA: Black restricted to points, red body (Bay)
Aa: Black restricted points, red body (Bay)

AtAt: Seal Bay (black is less restricted, resulting in a dark horse with reddish areas on the ‘soft areas: muzzle, over the eyes, elbow, flanks, in front of the stifle, back of buttocks).

Ata: Seal Bay (black is less restricted, resulting in a dark horse with reddish areas on the ‘soft areas: muzzle, over the eyes, elbow, flanks, in front of the stifle, back of buttocks).

aa: Black all over, it turns off all red when EE or Ee is present (ee only results in chestnut colour).

A+A+: Wild Type Bay (Mane and tail are black, may have some red. Black on points is limited to the fetlocks, or has red hair mixed in, not solid black lower legs)

A+A: Wild Type Bay (Mane and tail are black, may have some red. Black on points is limited to the fetlocks, or has red hair mixed in, not solid black lower legs)

A+a: Wild Type Bay(Mane and tail are black, may have some red. Black on points is limited to the fetlocks, or has red hair mixed in, not solid black lower legs)

*Wild Bay are uncommon to rare

  MC1RAGOUTI
EEAABayHomozygousHomozygous
EeAABayHeterozygousHomozygous
EEAaBayHomozygousHeterozygous
EaAaBayHeterozygousHeterozygous
    
eeAAChestnutHomozygousHomozygous
eeAaChestnutHomozygousHeterozygous
eeaaChestnutHomozygousHomozygous
    
EEaaBlackHomozygousHomozygous
EeaaBlackHeterozygousHomozygous

Other coat colour modifications:

There are links to other coat modifications we posted for the Equine Genetic Series (they appear as live links when you wave your mouse over the word).

SHADE: There is a gene responsible for how light or how dark the colour appears. It is not well understood, but researchers found an independent locus close to the ASIP locus. A different gene called the sooty gene can cause a coat to appear very dark, and dilutions such as the Cream or Dun gene lighten the coat of horses. But ALL horses have a base coat of Red or Black or the absence of both (white).

Bays of varying shade, McCullough Peaks, Wyoming

SOOTY: Some horses have the ‘sooty factor’ which can darken the coat of any horse. The genetics are not well understood (link to sooty).

PANGARÉ: Some horses have pangaré also called mealy where the soft areas (muzzle, over the eyes, elbow, flanks, in front of the stifle, back of buttocks) are light, or pale. (Link to pangaré)

FLAXEN: Commonly seen in chestnut horses, this gene lightens the mane and tail to a pale blonde color. Again, genetics are not well understood. Two bay horses can produce a chestnut with a flaxen mane, so it is possible it is present in bay horses genetically, simply not expressed (visible).

DILUTIONS:

  • Cream (Cr)
  • Pearl (Prl)
  • Dun (D)
  • Silver Dapple (Z)
  • Mushroom (Mu)
  • Champagne (Ch)

NONSYMMETRICAL WHITE PATTERNS

SYMMETRICAL WHITE PATTERNS

  • Appaloosa (Lp)

ADDITIVE WHITE PATTERNS

Common Bay, McCullough Peaks, Wyoming
Common Bay, Sand Wash Basin, Colorado
Common Bay with Sooty, Assateague Island, Maryland
Group of Bays, (and chestnut, buckskin, greys), McCullough Peaks, Wyoming
Bay (in front), Bay Duns behind, Pryor Mountain, Montana

Seal Bay. Although dark, note the red/lighter areas on the face, flank, elbow, stifle. McCullough Peaks, Wyoming

A non-fading black horse, note the color around the muzzle remains black. Little Book Cliffs, Colorado

Same horse with a Chestnut Dun. Note the lack of light areas. Non-fading black horses are uncommon, most black horses fade to a reddish-brown in summer, BUT the muzzle always remains black/dark. Little Book Cliffs, Colorado

Wild Bay, Assateague Island, Maryland (Also exhibits pangaré)

Wild Bay, Assateague Island, Maryland (same horse as above)
Personal note: Most of the Wild Bay types have orange hair at the base of the tail on top. You can easily see it here.

Wild Bay, Sand Wash Basin, Colorado

Wild Bay, Salt River Arizona (With pangaré: Note the pale muzzle, flank, stifle,)

Wild Bay and Wild Bay Roan, Salt River Arizona

Wild Bay, Salt River Arizona (same as above)

Wild Bay, Salt River Arizona (Note the legs have quite a bit of red/brown- they are not solid black).

Wild Bay, Sand Wash Basin, Colorado

Bays with Modified Coats

Bay Dun (Dun gene acting on a Bay coat lighten the coat to a golden colour, removing red. Black is not affected

Buckskin: One Cream gene acting on a Bay coat lighten the coat to a golden colour, removing red. Black is not affected. Onaqui/Great Desert Basin, Utah

Perlino (Two Cream genes acting on a Bay coat lighten the coat and mane/tail to pale cream, subtle darkening of the points are present (mane, tail lower legs). Onaqui/Great Desert Basin, Utah

Bay Roan. Onaqui/Great Desert Basin, Utah

Bay Roan. Pryor Mountain, Montana

Bay Tobiano Foal. Onaqui/Great Desert Basin, Utah

A famous Tobiano/Overo Bay, Picasso from Sand Wash Basin, Colorado (in memoriam)

Also, Picasso, making identification a challenge!

We hope you enjoyed the Bay Horses. Stay tuned for more exciting posts in the Equine Genetic Series brought to you by Karen McLain, Meredith Hudes-Lowder & Equus ferus Wild Horse Photography

References
Corbin LJ, Pope J, Sanson J, Antczak DF, Miller D, Sadeghi R, Brooks SA. An Independent Locus Upstream of ASIP Controls Variation in the Shade of the Bay Coat Colour in Horses. Genes. 2020; 11(6):606. https://doi.org/10.3390/genes11060606

Gower, J. (1999). Horse color explained: A breeder’s perspective. North Pomfret, VT: Trafalgar Square.    

Henry, M., & Dennis, W. (2017). King of the wind: The story of the godolphin arabian. Aladdin Paperbacks, an imprint of Simon & Schuster Children’s Publishing, Division.

Jacobs LN, Staiger EA, Albright JD, Brooks SA. The MC1R and ASIP Coat Color Loci May Impact Behavior in the Horse. J Hered. 2016 May;107(3):214-9. doi: 10.1093/jhered/esw007. Epub 2016 Feb 16. Erratum in: J Hered. 2016 Sep;107(5):479. PMID: 26884605; PMCID: PMC4885240.

Kathman, L. (2014). The equine tapestry: An introduction to horse colors and patterns. Charlotte, NC.: Blackberry Lane Press.  

Sponenberg, D. P. (1996). Equine color genetics. Ames: Iowa State University Press.

by Equus ferus Wild Horse Photography

Glossary of Terms: Genetics

Corona’s Band, Sand Wash Basin 2016

Cheyenne (in memoriam), Laramie, Can Wakan, Chipeta, Poppy (light chestnut front), Maybell (liver chestnut behind), Corona

Genetic diversity: Depends upon mutations, natural selection, gene flow, and genetic drift.

Genome: The complete set of chromosomes for an individual

Chromosome: a thread-like structure found in the nucleus of living cells. It contains deoxyribonucleic acid (DNA)

Gene: segments of DNA which are contained within in chromosomes

DNA:  Segments of base-pairs (adenine-thymine & cytosine-guanine). The order of these pairs form the structure of DNA

Allele: Two or more alternate forms of a gene. Examples are coat color modifier such as the Cream Gene. Horses can be dominant (CC & Cc), or recessive (cc). Some are more complex such as human blood types in which four possibilities exist (A, B, O, AB)

Single nucleotide polymorphisms: These SNP (also called ‘snips’) are changes within a single nucleotide. As an example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of DNA. These variations may be unique to one individual or they may be found in many individuals; scientists have found more than 100 million SNPs in human populations around the world. Most commonly, these variations are found in the DNA between genes. They can act as biological markers, helping scientists locate genes that are associated with disease.The SNIP’s are important in establishing genetic variability 

“An important part of the horse genome project was the identification of over a million SNPs, which directed the development of genomic tools for mapping in the horse. The SNPs were generated from the diploid genome of Twilight and by partial sequencing of seven additional horses of diverse breeds. The reference assembly and the SNP map marked a turning point in horse genomics by providing resources for driving subsequent molecular, clinical and evolutionary studies in the horse” (Raudsepp, 2019)

“Twilight”, a Thoroughbred mare, was the first horse to have her entire genome mapped in 2006-2007

By Doug AntczakBaker Institute for Animal HealthCollege of Veterinary Medicine Cornell University – http://www.genome.gov/pressDisplay.cfm?photoID=20008, Public Domain, https://commons.wikimedia.org/w/index.php?curid=13811633


Genetic diversity: The range of different inherited traits within a species.

Mutation:  Changes in the sequence of DNA. They can be a tiny as one nucleotide change (adenine-thymine & cytosine-guanine) or consist of a larger part(s) of the gene. They occur frequently (1 per 1,000 nucleotides) which equates to 4-5 million per genome (the complete set of chromosomes per organism). Most are benign and cause no problems (disease or disability) for the organism, but some can be lethal (lethal white [foal] syndrome).  Some mutations can be advantageous such a gene coding for harder hooves in wild horses. Soft hooves could potentially render a horse lame which might make them more susceptible to predation (an example).

Natural selection: The process in which certain genes occur in better adapted horses. Individuals with mutations that are better adapted for survival pass these traits to their offspring. The mutations are inherited characteristics that allow a horse to adapt to the environment more successfully . Presently, there is no significant difference between the genome of wild horses and their domestic counterparts.

Gene flow: This refers to the migration of organisms, and the genes they carry, from one population to another. It can occur by physical movement (migration), or human mediated translocation of some horses from one management area to another.

Genetic Drift: The totally random process which changes the numbers of gene variants in a population. Genetic drift takes place when different forms of a gene, called alleles, increase and/or decrease by chance over time. Allelic frequencies measure the presence of these variations. It is common for genetic drift to occurs in small populations, because infrequently occurring alleles face a greater chance of being lost because they occur rarely. During the process of genetic drift, rare alleles are lost and the common alleles become the only allele at a particular locus. Both possibilities decrease the genetic diversity of a population. Genetic drift can result in the loss of rare alleles and decrease the gene pool.

Microsatellite markers:  These are repeating sequences of DNA (or microsatellites) and are distributed throughout the genome and passed on to the organism’s offspring. They are useful in determining paternity, as well as measuring the relatedness between individuals of a population and useful for determining genetic variability.

Patrilineal: Kinship derived from the male or father lineage

Matrilineal: Kinship derived from the female, or mother lineage

mtDNA (Mitochondrial DNA): This form of circular DNA is found in the mitochondrial cells (the ‘powerhouse of the cell’… shades of high school biology class). mtDNA is passed from mother to offspring of both genders and is very useful in determining ancestry by following the maternal lineage back in time. It plays a role in the controversy surrounding wild mustangs and the Spanish Colonial horse type.

Patrilineal Y Chromosome Analysis (Male Specific Region of the Y Chromosome- MSY): Every male horse inherits a Y chromosome from their father. Similar to matrilineal mtDNA, the male horses can trace their lineage back hundreds of years. Researchers look for mutations (which are found in many chromosomes, not just the Y chromosome). These changes in the genetic sequence are called ‘polymorphic markers’ and are useful because they are passed down from father to son on the Y chromosome to trace patrilineal ancestry.

References

Raudsepp, T., et al. “Ten Years of the Horse Reference Genome: Insights into Equine Biology, Domestication and Population Dynamics in the Post‐Genome Era.” Animal Genetics, vol. 50, no. 6, 2019, pp. 569–597., doi:10.1111/age.12857.

by Equus ferus Wild Horse Photography

The Dun Dilution Factor

Dun foal “Luna” (second) belonging to Connie Rivas of HP Quarter Horses

The Dun Dilution Factor works on all horse colours. It can appear in black, bay, chestnut, palomino, buckskin, cremello, roan, and even appears in grey horses prior to the horse greying out. Like the Cream Gene, the Dun Dilution lightens the base coat colour, adds primitive markings, but leaves black colour alone. There are so many different shades of dun and the nomenclature varies between horse breeds and regionally. We will describe them related to their base color. Black horses are unique because the resulting dun horses have a specific name called grullo/grulla. Dark bays and blacks can be almost impossible to distinguish.

A black horse with a Dun Dilution turns the horse a lighter shade, with primitive markings, and guard hairs (lighter hairs on the outside of the mane and tail). The head is usually darker. The resulting horses have a slate-blue with less red present although some can have a warm tone. They generally have a very dark head. Without genetic testing, we are only guessing at the actual chromosomes of these horses. .

Primitive markings are named for markings found on ancient horse breeds such as the Przewalski or Tappan horse. They include a continuous line from the withers to the dock (top of the tail). Other markings include wither and/or neck stripes, cobwebbing: faint stripes on the face, zebra stripes on the legs, chest stripes, and darker ear tips. Zebra stripes are the colour of the underlying coat color, so a chestnut horse has darker chestnut stripes and a bay has black zebra stripes. Lighter hair on either side of the mane and each side of the tail, called ‘guard hairs’ may also be present.

The management are with the most Duns relative to the population is Pryor, they are plentiful there. Sand Wash Basin has many as well, and they are present at the Salt River. Little Book Cliffs has them, but McCullough Peaks does not have many. Great Desert Basin also does not have a large population. The Dun trait is autosomal dominant:

From UC Davis (they do genetic testing in equines)

Alleles: D = Dun dilute, nd1 = Non-dun 1, nd2 = Non-dun 2

Horses with nd2/nd2 genotype will not be dun dilute and will not have primitive markings. They cannot transmit a dun dilution variant to their offspring.

Horses with nd1/nd2 genotype will not be dun dilute, but may have primitive markings. They may transmit the non-dun 1 variant to 50% of their offspring.

Horses with nd1/nd1 genotype will not be dun dilute, but may have primitive markings. They will transmit the non-dun 1 variant to all of their offspring.

Horses with D/nd1 or D/nd2 genotype will be dun dilute and will display primitive markings. They may transmit the dun dilute variant to 50% of their offspring. Matings with N/N genotype will results in a 50% chance of producing a dun dilute foal.

Horses with D/D genoytpe will be dun dilute and will transmit the dun dilute variant to all of their offspring. Matings with any genotype are predicted to produce dun dilute offspring.


(Click on all the photos to enlarge them)

A typical Bay dun
Black horse becomes a “grullo (male) or grulla (female)
Bay horses become a yellow-tan shade with their points (legs, mane, and tail remain black)
Left photo: Bay horse. The photo on the right shows a dun in front and a bay to the right. Note the reduction of red, resulting in a more warm golden colour
A solid chestnut horse becomes a lighter, golden horse with deep red points
A chestnut horse with a flaxen mane and tail becomes a lighter Dun -note the reduction of red
A liver chestnut horse becomes a deeper, darker Liver Chestnut Dun
Some dorsal stripes have marks perpendicular to the stripe, like hatch marks. Also, note the prominent wither marks and some neck marks.

A nice example of a line-back dorsal stripe in a Grullo Mustang

Well-marked wither and neck marks in a bay dun.
Duns can be very pale, such as this “buttermilk” dun on the right. Base colour buckskin, or light bay. A grullo is the second from the left.
A nice red dun on the left, and pale dun to the right
Duns can occur in buckskin horses- they are usually tan and hard to distinguish from more yellow duns. Genetic testing may reveal their genes. In this photo, we have three shades of Dun. The horse in the top right may be a Dunskin
A family of Duns. The foal is a Chestnut dun (chestnut base), the Stallion is a Chestnut dun, and the mare is a Bay dun
Bay dun mare with a red dun foal
The same pair as above- note the dark ear tip on the foal characteristic of duns. Other colors may have dark ear tips, so this alone is not a way to determine a dun
Two duns (Black dun, then a Bay Dun), a bay, and a roan bay peeking a head over the last horse…
This foal looks like a dun, but never trust a foal coat… they change constantly.
This is a dun that is greying out. Eventually, the dorsal stripe and zebra stripes will fade as the horse whitens with age
Feeling confident about your ability to spot Duns? There is one Dun in this photo
And one Dun in this photo… This might be a Dunskin
A pale Chestnut, a darker Chestnut, a bay and a roan- a comparison of red colours.
A Dunalino (Palomino + Dun, note the dorsal stripe, zebra stripes on the legs, and shoulder markings. This is Corona of Sand Wash Basin. Next to him is a Chestnut Dun pinto named Little Thunder: note the zebra stripes on the front legs, a dorsal stripe), and a chestnut behind.
Two Grullos/dark bays of different shades…
A warm dun base coat is most likely a dark chestnut base.
A pale dun, bay base (because it has black points)
A gorgeous red dun stallion on the left- probably liver chestnut base and a dark warm grullo/dark bay. Grullos tend to have very dark heads
Some call this shade a peanut butter dun
Warm grulla/dark bay mare- gravid
A pale grulla, often referred to a silver dun
Dark grullo/dark bay- may be a lobo dun
Dark grullo and a bay roan
Corona from Sand Wash Basin is a Dunalino or a Dun Palomino
One Chestnut Dun and two pale duns- possibly Dunskins (Buckskin + Dun)
Two handsome red duns; note the slightly darker red zebra stripes on both stallions

A Bay Dun Roan- with a Chestnut Dun foal. Dun roans often have paler dorsal stripes (the stallion off to the right is a Black Roan).
You can appreciate the zebra stripes and how they reflect the underlying colour in the dun bay roan. She also has faint spider webbing on her face in a diamond shape around her forehead.
Bay dun roan
Bay Dun roan
A Liver Chestnut Roan in front, with a Bay Dun Roan behind.
The Bay Dunstallion at the top of this image demonstrates the guard hairs as they travel down the mane, across the back, and into the tail. Three Bay duns and a blue Roan
A grulla in front, a bay dun, and a normal bay- you can appreciate how much red is reduced in the dun when compared to a bay
It’s an interesting Bay Dun, possibly a Dunskin from Onaqui.
Same horse from the back

Horses that look like Duns, but aren’t…

Two buckskins- they resemble duns but lack zebra striping and a dorsal stripe. The mare looks like she has a dorsal stripe, but it is fuzzy and incomplete.
Same pair from the side
The Blackroan looks like he has a dorsal stripe, but it is pale and incomplete. There are also no zebra stripes.
A beautiful buckskin mare (yes, this is a mare) with a similar yellow-tone coat
The Bay Roan in the back (top) is normal; the buckskin roan may be a dun- roans are sometimes hard to distinguish from dun roans because the roaning pattern may obscure the dorsal stripe and create a pattern similar to zebra stripes.
A buckskin greying out resembles a warm grullo- there are some faint zebra stripes and perhaps some wither and neck marks… only genetic testing will confirm
The first horse is bay, and the second has a faint dorsal stripe and guard hairs, potentially making it a pale Bay Dun; the third horse is a Bay Dun Roan, and the last horse is a Bay Dun.
Same group as above with a bay roan at the back and remember, never trust a foal coat.
Sometimes, wild horses make the identification of coat colour a challenge…
Answers to the who’s who…

Bibliography
Gower, J. (1999). Horse color explained: A breeder’s perspective. North Pomfret, VT: Trafalgar Square.    

Kathman, L. (2014). The equine tapestry: An introduction to horse colors and patterns. Charlotte, NC.: Blackberry Lane Press.  

Sponenberg, D. P. (1996). Equine color genetics. Ames: Iowa State University Press.

by Equus ferus Wild Horse Photography

The Cream Dilution Gene (updated)

Two Palomino Stallions spar at Sand Wash Basin
©Equus ferus -Wild Horse Photography

The Cream Gene is a modifier, or a gene that acts on one of three base colours in horses.  The three base colour are chestnut, bay, and black. Some people classify brown as separate colour but for the purposes of this discussion, we will group brown with black since the inheritance is the same.

(PLEASE TAP/CLICK ON THE PHOTOGRAPHS TO VIEW A LARGER VERSION)

A band with Palominos and buckskin race across Sand Wash Basin

The Cream Dilution can either be expressed as a single dilution, or a double dilution. Every chromosome has two alleles that represent the way in which each chromosome is inherited and you receive one allele from each parent. Simply put, the chromosomes (usually represented by letters) appear in pairs. To review high school biology, these pairs are generally dominant or recessive. Dominant genes are represented by two capital letters or one capital and one lower-case. The animal appears the same (phenotype) whether they are EE or Ee. The recessive form is represented by two lower-case letters ee.

The cream gene in the single form acts upon chestnut, bay and black by diluting the red colour to cream. The Cream Colour may be light enough to appear almost white to a dark chocolate tan colour. The black is generally unaffected so bay horses horses retain the black points, and mane/tail. Black horses appear somewhat diluted- a mousey chocolate. Horses with a single Cream dilution generally have dark eyes (unless blue from paint patterns) and black skin except where there are white markings (paint markings, facial markings, and leg markings).

Corona’s Band
There are six cream horses
Sand Wash Basin, Colorado
©Equus ferus -Wild Horse Photography


The double dilution, or two Cream Genes acts upon both the red and black colours. The red become light cream/off white, and the black lightens to cream. In a bay horse with two cream genes, the body colour is light cream and the points appear as a darker shade of cream. Smokey Black Creams have a slightly over all darker shade but without genetic testing, it is impossible to determine what the base colour is in these horses. All double dilute Cream horses all have pink skin and blue or light green/hazel eyes.

The double dilute horses (Cremello, Perlino & Smokey Cream) are difficult to distinguish by appearance or phenotype alone. It is possible the double dilutes are all cremellos, or perlinos- or they are dirty. Google Perlino, Cremello, or Smokey Cream to see how they truly look- they are stunning colours.

The “Sooty” modifier is a additional genetic trait in which the horse’s coat looks like someone airbrushed darker colouration over the coat. In some extreme cases, the sooty modifier can turn a palomino so dark it appears ‘chocolate’ coloured- as in the case of Cloud’s son Bolder (photos below). Sooty can occur in any color and is believed to help break-up the outline/contour of a horse (countershading) and making it harder for predators to estimate the distances of the their prey.

Echo (Palomino) and his sire Bolder (Sooty Palomino) spar
Pryor Mountain, Montana
©Equus ferus -Wild Horse Photography

Cream dilutions can also appear with other dilutes such as Dun. The resulting horses are called Dunalinos (dun + palomino) and Dunskins (dun + buckskin). It can be a challenge to tell pale palominos from cremellos/perlinos horses, but look at the muzzle and other mucous membranes (grey in Palomino, pink in creams). Watch for facial markings which also appear pale-pink even on palominos. The eyes are usually dark in Palominos, and pale green or blue in Creams.

BASEONE CREAM GENETWO CREAM GENES
BAYBUCKSKINPERLINO
CHESTNUTPALOMINOCREMELLO
BLACKSMOKEY BLACKSMOKEY CREAM
Bay- Base Coat

Buckskin (varying shades) BAY + ONE CREAM GENE= BUCKSKIN

Perlino BAY + TWO CREAM GENES= PERLINO
Chestnut (BASE)
Palomino
CHESTNUT + ONE CREAM GENE= PALOMINO
Cremello
Palomino
CHESTNUT + TWO CREAM GENE= CREMELLO
Black (BASE)
Smokey Black Dun (Buckskin behind)
BLACK + ONE CREAM GENE= SMOKEY BLACK
Smokey Cream
BLACK + TWO CREAM GENE= SMOKEY CREAM

Chestnuts

Chestnut with sooty- appears most prominently in the mane and tail, base colour is chestnut.     Cimarron Sand Wash Basin ©Meredith Hudes-Lowder Equus ferus -Wild Horse Photography    

 

Corona- Palomino + Dun= Dunalino
Note the primitive markings (black arrows) and typical palomino colouration
Sand Wash Basin, Colorado
©Equus ferus -Wild Horse Photography

Palomino- mid colour
Bobby
Sand Wash Basin
©Meredith Hudes-Lowder
Bobby (2)
Sand Wash Basin
©Equus ferus -Wild Horse Photography

Palomino- Light
McCullough Peaks
©Equus ferus -Wild Horse Photography

  Buckskin Stallion with two light palominos in his band Buggs Band Sand Wash Basin
Buggs is a buckskin, and note the dark eyes on the paler palominos
©Karen McLain Studio
Cloud- a well-know Palomino (in memoriam)
His son is Bolder (sooty palomino below)
His grandson Echo (pale palomino below)
Pryor Mountain
©Equus ferus -Wild Horse Photography

Palomino with Sooty Bolder Well known for changing colour as he aged, Bolder has the Sooty gene expressed almost to the maximum. Born lighter, each year he grew darker and darker.  Some liver chestnut horses that have a cream gene are called “chocolate palominos” and may be hard to distinguish from Sooty palominos but the chocolate palominos tend to be browner and the colour is more uniform and not scattered as we see here on Bolder.   Pryor Mountain ©Karen McLain Studio Equus ferus -Wild Horse Photography    

Palomino with sooty- Bolder and his son Echo, a light palomino Pryor Mountain
©Karen McLain Studio

(Left) Light Palomino Echo, (Right) Sooty Palomino Bolder
Sire -right, Colt – left
Pryor Mountain
©Karen McLain Studio
(Rear) Palomino with sooty restricted to the forelegs, face, and chest.
(Front) Tripod, a cremello- note the pink skin around his muzzle.  
Sand Wash Basin
©Karen McLain Studio Equus ferus -Wild Horse Photography    
Pale Palomino Foal “Isabella”
Sand Wash Basin
©Equus ferus -Wild Horse Photography
The pale cream color was so highly prized by Queen Isabelle de-Bourbon that they became known as Isabella Palominos. Only royalty were allowed to own this beautiful golden colour.
Elisabeth of France or Isabella of Bourbon (22 November 1602 – 6 October 1644) was Queen Consort of Spain (1621 to 1644) and Portugal (1621 to 1640) as the first spouse of King Philip IV of Spain. Queen Isabella gifted some gold horses to Juan de Palomino which is where this color gets its name. Note the grey muzzle and dark eyes indicating this ia a pale palomino.
(https://baroquehorse.com.au/history-of-the-isabella-horse/)
Meteor – Palomino Tovero Sand Was Basin

BAYS

Sooty Bay  
McCullough Peaks
©Equus ferus -Wild Horse Photography  

                 

YELLOW ARROWS= Bay with Sooty PINK ARROW= Bay GREEN ARROW= Primitive Bay or Bay with Pangaré or a lightening over the soft area- muzzle, flanks, eyes, stifle) .A wild Bay is a bay with paler colour and the black points of the legs do not extend above the knees/hocks- often paler in comparison.   McCullough Peaks ©Karen McLain Studio Equus ferus -Wild Horse Photography      

YELLOW ARROWS= Bay with Sooty   PINK ARROWS= Bay McCullough Peaks ©Karen McLain StudioEquus ferus -Wild Horse Photography TM

Buckskin Stallion Sand Wash Basin
Buggs
©Karen McLain Studio
Buckskin Tobiano Yearling
In spite of a blue eye- her black mane, partial black tail and dark muzzle indicate she is a buckskin.
Great Desert Basin
©Equus ferus -Wild Horse Photography
A Dunskin, or Dun + Buckskin
Note the primitive markings (wither marks, zebra stripes on his legs)
Great Desert Basin, Utah
©Equus ferus -Wild Horse Photography

Buckskin Mare with her Cremello colt    
McCullough Peaks
©Equus ferus -Wild Horse Photography TM

Buckskin Mare- slight Sooty    
McCullough Peaks
©Equus ferus -Wild Horse Photography TM

Sooty Buckskin
McCullough Peaks
©Equus ferus -Wild Horse Photography

Always identify the cream variant before the mud bath
Echo (Cloud’s Grandson)
Pryor Mountain, Montana
©Equus ferus -Wild Horse Photography

 

Genotype at the agouti locusChestnut horsesPalomino horses
A+_Light chestnutCream palomino
AA_Red chestnut, with AAAA being the reddestGolden palomino
At_Standard chestnutSeasonal palomino
Aa AaLiver chestnutChocolate palomino

 Bibliography
Gower, J. (1999). Horse color explained: A breeder’s perspective. North Pomfret, VT: Trafalgar Square.    

Kathman, L. (2014). The equine tapestry: An introduction to horse colors and patterns. Charlotte, NC.: Blackberry Lane Press.  

Sponenberg, D. P. (1996). Equine color genetics. Ames: Iowa State University Press.

Presented by Dr Meredith Hudes-Lowder

by Equus ferus Wild Horse Photography

The Grey Modifier

The Grey Modifier
The grey modifier isn’t an actual colour; it is the loss of color. Grey horses begin life normally coloured and progressively lose pigment throughout their lifetimes, retaining dark skin colour. The base colour of a grey horse can be any coat colour or pattern.  In general, foals are usually born a few shades lighter than their adult colour, but grey horses are born dark. Percheron breeders often say, “a black horse is born grey, and a grey horse is born black” (Sponenberg, 2017). Because of this dark coat, it may not be possible to determine the foal’s base colour (chestnut, bay, brown or black). In addition to a darker foal coat, an indication a foal will turn grey as an adult are rings of white around the eyes often referred to as “grey goggles”.
(Click on the photo and you will see a larger gallery)

  • Charming pattern on a dun greying out
  • Grey goggles on a dun/sorrel
  • Grey goggles on a dun/sorrel


The grey coat colour is due to the presence of a dominant gene (G) at the grey locus on the twenty-fifth chromosome. Grey is epistatic to all coat colour genes except white, which means the grey gene overrides normal coat colour. A grey horse must have at least one grey parent. In a horse of more than one colour: paint, tobiano, overo, pinto etc), the grey colouration will act upon the solid colour and leave the white areas alone. Eventually, the horse will look white all over, except when it rains or in good lighting. These “ghost paint” horses are hard to spot, but once you have seen a few, you’ll begin to recognize them.

Ghost Paints/Pintos

  • Tobiano grey
  • Splash white possible grullo &dun
  • Frame overo “ghost paint”

As each coat sheds out, a grey horse will become lighter and lighter. The speed with which a horse attains a fully white coat is extremely variable, but it is inherited. Because greying time is hereditary, some horse breeds were selectively bred to turn white swiftly such as the Lippizaner horses and Kladruber (Danish Royal Horses), while the Percheron draft horses take much longer to whiten.  The underlying coat colour also plays a role in the length of time required to lighten simply because a lighter horse such as a palomino will appear lighter faster than a dark bay horse.

On an individual horse, the areas that lighten first are also variable but there is a general pattern that most grey horses follow. There are always exceptions to this generalization.

BEGINS:
Face (except forehead, nasal bones & lower edges of the cheek)
Tail -usually begins in the lower half of the tail
Coronet- some grey horses have a pale ring around the coronet
Throat- jugular notch (the distinct groove where the throat meets the head)
Chest
Elbows- behind the elbow
-At this point dapples will appear if a horse is prone to dappling along the shoulders, sides, and neck. The dapples spread and eventually all that remains dark are the knees, hocks and hindquarters which lighten last (Kathman, 2012).

Some horses remain partially coloured all their lives, and some never achieve white. Horses with facial markings, such as a star or blaze, will start to grey outwardly from the marking. The blaze will spread as the face lightens.

  • Two greys- the front stallion with a browner/warmer tone
  • Cypress- note the blaze starting to expand in the center
  • The foals’s blaze is beginning to expand laterally

Not all horses dapple, many simply lighten progressively and more uniformly over time. Some horses have areas of white amidst darker grey colour. A Thoroughbred named Tetrarch was known for these white spots and for reviving the dwindling number of grey Thoroughbreds (Gower, 2016).  A discussion of grey horses in racing history can be found here:

  • The Tetrarch

I proudly own & ride a rescued grey Off-the-track-Thoroughbred (OTTB) named Ashe.

  • Ashe & Jess jumping
  • Ashe and I jumping

“Grey horses progressively acquire white hairs throughout the coat as they age, and the greying process (rate and location) varies from horse to horse. Some horses will grey first in the mane and tail hairs while others will lose pigment last in the mane and tail (Sponenberg 2009). Additionally, some horses will retain small flecks of pigmented hairs to display a ‘flea‐bitten’ appearance , while others will retain pigmented hairs that outline areas of depigmented hairs to display a ‘dappled’ appearance. Furthermore, some grey horses will develop skin depigmentation (similar to vitiligo in humans) in addition to hair depigmentation (Sutton & Coleman 1997). It is speculated that some of the horse to horse variation in the greying process is likely due to modifier genes that have not yet been investigated. ‘Grey’ is said to be epistatic to all other coat colours and patterns, as horses that inherit the grey duplication will eventually lose pigment as they age, and any underlying coat colour or pattern will be masked by ‘grey’ ” (Thiruvenkadan, Kandasamy, & Panneerselvam, 2008).

Flea-bitten greys are horses with small flecks of a darker colour intermixed in the coats. The mechanism for this trait is unknown although most flea-bitten speckled horses are heterozygous (Gg). A flea-bitten horse bred to a non grey horse may result in offspring that are flea-bitten indicating the trait may be separate but linked to the grey color (Bailey & Brooks, 2013).

Of note, grey horses are prone to a type of melanoma which is not cancerous and does not results from exposure to sun. These tumours grow all over the body and are common in mucosa (mouth, rectum/anus, sheath), but can be found anywhere in the body. They normal pose no threat unless the tumours block major blood vessels, grow on vital organs, or interfere with quality of life for the animal.

Grey horses with black manes & tails

  • Black mane and tail- already starting to lighten Note the blase expanding as well
  • Dun Grey- note the primitive markings (zebra striping & dorsal stripe)

Grey horses with white manes & tails

  • White mane & tail
  • White mane & tail
  • White mane & tail

Grey horses with black manes & white tails

  • Black mane & white tail
  • Black mane & white tail
  • Black mane & white tail

Pure grey or white

  • White
  • White & Flea-bitten
  • White & Flea-bitten
  • All white- sometimes referred to as ‘porcelain’
  • White left & Rose Grey right
  • Old timer & friend Note the dark horse’s blaze is expanding slightly- this is likely due to age, not grey- both these stallions are well into their twenties
  • Grey Mare & foal greying
  • Grey- liver chestnut base Very uniform in grey coloring
  • Two greys- the front stallion with a browner/warmer tone
  • Two greys
  • Uniform grey- note the expaning star-stripe

Foals & Yearlings transitioning to grey

  • Charming pattern on a dun greying out
  • Splash white possible grullo &dun
  • Grey goggles on a dun/sorrel
  • Grey goggles on a dun/sorrel
  • Grey Mare & foal greying
  • Grey goggles on a dark foal
  • Flea-bitten mom & foal starting to grey
  • Cream, grey & rose grey Note the creamy colour of the larger horse in back as well as the pink muzzle
  • Bay grey- note the blaze expanding

Grey Pintos

  • Frame overo “ghost paint”
  • Grey head- note the faint blaze outline
  • Splash white & Rose Grey (possible dun)
  • Ghost paint
  • Faint outline- Frame Overo

Half tails

It is not uncommon for the tails of grey horses to whiten unevenly forming a “half tail”

  • Black mane & white tail
  • Light Dun Grey

Dappled Greys

Interesting transitions

Horses such as duns, or light chestnuts often grey in an amazing variety of shades. Rose greys are chestnuts that go through a light pale red phase- hence the term rose grey

  • Light Dun Grey
  • Brownish-rose grey Note the expanding blaze
  • Splash white possible grullo &dun
  • Dun Grey- note the primitive markings (zebra striping & dorsal stripe)
  • Note the primitive wither, zebra stripes, and neck marking
  • Pale dun grey
  • Pale dun grey
  • Buckskin/dun grey
  • Cream, grey & rose grey Note the creamy colour of the larger horse in back as well as the pink muzzle

Greys in groups

Freeze brands

Mustangs are identified by a freeze- brand on the neck. It normall leaves hair white. They are visible in grays, just more challenging to see.

  • Freeze brand
  • Normal color (buckskin) with freeze brand

Not Greys

Many coat colours such as roan, grullos, and cremello/perlino may be mistaken for grey. Roans and grullos retain dark heads throughout their lives. Cremello and perlinos have pink skin- especially noticeable around the muzzle.

  • Cream & Grey
  • Cream, grey & rose grey Note the creamy colour of the larger horse in back as well as the pink muzzle
  • Liver Chestnut Roan
  • Muddy dark bay

Flea-bitten Greys

References
Bailey, E., & Brooks, S. (2013). Horse Genetics (2nd ed.). Boston, MA: CABI.

Gower, J. (2016). Horse Color Explained. Brattleboro, VT: Echo Point Books & Media.

Kathman, L. (2012). The Equine Tapestry (Vol. Volume 1- Draft and Coaching Breeds). Charolette, NC: Blackberry Lane Publishing.

Sponenberg, D. P. B., Rebecca. (2017). Equine Color Genetics (4th ed.). Hoboken, NJ: John Wiley & Sons Inc- Blackwell.

Thiruvenkadan, A. K., Kandasamy, N., & Panneerselvam, S. (2008). Coat colour inheritance in horses. Livestock Science, 117(2), 109-129. doi:https://doi.org/10.1016/j.livsci.2008.05.008





by Equus ferus Wild Horse Photography

The Frame Overo

When I first sat down to go through my photographs, I was hoping to have five or six good examples of the Frame Overo trait. I was pleasantly surprised to find so many mustangs with this particular pattern. Interestingly, I found Frame Overo mustangs principally at Sand Wash Basin and Black Hills Wild Horse Sanctuary. It is entirely possible there are some Frame Overos at other management areas, but neither Karen nor I had photographed any of them. The Frame Overo is also unique to North America. This pinto pattern is common only in Spanish Colonial Horses or their descendants. However, the trait occasionally, but rarely. appears in European-derived horses such as Thoroughbreds, Ethiopian breeds, and miniature horses (Sponenberg, 2009).

Frame Overo horses that have white patches superimposed on a background of any base colour such as roan, bay, chestnut, palomino and so on. The white colour often begins as a patch on the neck or barrel and spreads horizontally. The back almost always remains solid coloured between the withers and tail. The white patches are irregularly edged and splashy (Bailey & Brooks, 2013) although some white markings are clean and crisp, similar to tobianos (Sponenberg, 2009). The markings usually do not have the lacy or frosted appearance of Sabino patterned horses (Kerson, 2015)

The tail is generally one colour and at least one leg is usually solid coloured although often all four legs are solid. If the legs are solid, they may have socks or stockings in a pattern one might find on a non-pinto horse. The markings on the head are often extensive, bonnet or apron-faces are common. Additionally, they may have a pigmented upper or lower lip, or ‘moustache’ (Sponenberg, 2009).

The genetics are simple, the Frame trait is autosomal dominant, which means a Frame foal must have one Frame parent. However, if both parents have the Frame gene, there is a 25% possibility the foal will be homozygous and have two Frame genes. This foal will not survive because a homozygous Frame is linked to another genetic defect which causes loss of peristalsis (the wave-like action that moves food through the intestines), or more rarely, an incomplete colon. (Bailey & Brooks,2013). More information and examples are located at the bottom of this page.
FF= Normal color
Ff-= Frame Overo
ff= Overo Lethal White

Perhaps one of the best-known Frame Overos is Picasso from the Sand Wash Basin. This handsome Bay horse is one of the most photographed mustangs and he has a Breyer Horse modelled after him. He is a Bay Frame Overo (and possibly carries other pinto traits). Many of his numerous offspring are Frame Overos including two know Lethal White foals. There will be more information on this genetic anomaly presented below.
Picasso
Picasso
This is an excellent example of a Bay Frame Overo stallion.
Note the white markings on neck and barrel as well as the four solid coloured legs.
Sand Wash Basin, Colorado
The horse on the right is a Chestnut Frame Overo
Sand Wash Basin, Colorado
A small family band with a Sorrel Frame Overo Stallion and a Frame Overo foal. In the management ranges, we cannot be certain of a foal’s parentage. Identifying a foal’s dam is generally more reliable than the sire. However, mares have been known to steal foals from other mares. Additionally, fillies will leave their natal bands briefly, breed with another stallion, and return to their natal band to deliver and raise the foal within the band they were born. Without genetic testing, we cannot be certain.

Hoot, Juniper, and Pinyon (2014)
Sand Wash Basin, Colorado
A Chestnut Frame Overo. The pigmented lip is common and may appear on the upper lip, lower lip, or both as this mustang demonstrates.
Sand Wash Basin, Colorado
The Chestnut Frame Overo is unusual because the right hind leg is extensively marked with white. This may be an anomalous finding, or an indication there are other pinto genes present, possibly Sabino. The heavily white face and body markings are more characteristic of Frame Overos.
Sand Wash Basin, Colorado
This charmingly marked dark (liver) Chestnut Frame Overo mare is called ‘Crazy Horse’. The freckles on her face are also known as Belton Spots and similar to the spotting found in English Setter dogs. Many horses with Belton Spots on their facial markings, also show “ermine spots” on their legs.  From Sand Wash Basin.
Although not perfectly focused, this Bay Frame Overo has Belton spots on his blaze as well as ermine spots (black spots on socks that are usually found along the coronet band). The ermine spots can cause the hoof to darken and appear striped. From Sand Wash Basin
These two beautiful sparring stallions are from Sand Wash. Kiowa on the left (Bay) and Haze on the right (Sorrel). Haze is a minimally marked Frame Overo- can you find the tiny white mark on Haze?
This is Miss Fleck- she is a Chestnut Frame Overo from Sand Wash Basin: the first image is her as a foal, the second image as a young mare. She was born into Voodoo’s band a but later joined Picasso’s band (2013). Picasso has since lost his band but he has been doing well as a bachelor. Fleck gave birth to a Lethal White Foal.
Fleck: foal, right side
Fleck: left side
This is Kiowa from the near side (left) from Sand Wash Basin. He had just been in a fight and you can see lacerations on his hip and shoulder. There is also a significant scar on Kiowa’s left haunch just below the laceration. It is believed he tangled with either a mountain lion or a wound from fighting that became infected. It is also possible he ran into a fence along the border of Sand Wash Basin and neighbouring ranches.
This is Raindancer. A lovely Chestnut Frame Overo with blue eyes from Sand Wash Basin.
This is an excellent example of a Bay Frame Overo mare from Sand Wash Basin, Colorado with a pigmented lip, flank markings and a small lower neck/shoulder marking.
Here is a lovely colt Named Van Gogh, he is one of Picasso’s many Frame Overo offspring from Sand Wash Basin.
This is Yatzee on the left and a grey stallion on the right from Sand Wash Basin. The grey is actually a Frame Overo – if you look closely at his neck, you’ll see the faint outline of the original white mark in the middle, just under his mane. He also has some white markings on his barrel. Some people refer to grey pinto as “ghost paints/pintos”. In the winter it is impossible to tell them apart from solid grey colour horses. A wet grey pinto in a summer coat is the easiest to recognise because you can see the underlying skin colour: pink under white markings and darker under the base colour
Another “Ghost- Frame Overo Grey from Sand Wash Basin. The horse on the left has several white Frame markings on his neck, barrel and just above his stifle. He also has the distinctive white apron face with the pigmented lip. The pink skin of the white marking is especially noticeable on this horse’s muzzle. If you see a horse with a pigmented lip, there is a good chance they are a pinto- often a Frame Overo. The middle horse is also a Frame Overo, this time black with four white stockings.  Four white stockings may indicate this mustang has other pinto genes.  The last horse is a Bay Frame Overo with a usual number of white leg markings. Generally, the leg markings do not rise above the knees in Frame Overos.
This family band has two Frame Overos from Sand Wash Basin. The foal, a chestnut beginning to grey-out, and the sorrel stallion. Again, notice the solid coloured legs which help distinguish Frame Overos from Tobiano pinto.
A handsome Grullo Frame Overo gelding from Black Hills Wild Horse Sanctuary Black Hills is a wonderful rescue organisation, please click on the link to find out more
A Black Frame Overo from Black Hill  Wild Horse Sanctuary
Bay Frame Overo with a stunning pattern from Black Hill  Wild Horse Sanctuary.
Two Black Frame Overos from Black Hill  Wild Horse Sanctuary. Note the tendency for Frame Overos to have solid colour on the spine from the withers to the dock.
Sugar, a Grulla Frame Overo from Sand Wash Basin, Colorado
This stallion is a Chestnut Frame Overo from Sand Wash Basin. It is evident he is thin but these horses receive no care. Many of the horses are underweight from untreated injuries, dental issue, and other injuries or infections that go untreated. It is truly survival of the fittest and only the strongest survive to reproduce. He was a very fiesty stallion, sparring with the bachelors and band stallions.
A dark chestnut Frame Overo pinto from Sand Wash Basin with very little white on his belly (the rest is dried mud)- referred to as a minimal Frame Overo. This stallion is called Spyder.
A Minimal Dun Frame Overo pinto from Sand Wash Basin.
This beautiful grey colt is a minimally marked Frame Overo. All four legs are solid and there is no white mark on either side. According to Sponenberg (2013), this horse will sire horses with varying amounts of white. Becuase of the lethal white syndrome, any Frame Overo owner should test both horses prior to breeding to avoid the chance of a foal that will not survive. Sand Wash Basin, Colorado
A minimally marked Black Frame Overo from Sand Wash Basin named Spyder.
A beautiful Black Frame Overo from Sand Wash Basin named Lightning. He was believed to be over 35 years of age at his death. He is one of the stallions responsible for the Frame Overo trait becoming so prevalent at Sand Wash Basin. He lived all his years free running amongst the Colorado sage.
A minimally marked Bay Frame Overo from Sand Wash Basin with very little white and four solid legs.
Another Minimal Frame Overo Chestnut. This is Mimi, she is a foal by Picasso and out of Mingo (2012). She has white socks but they are normal height one normally associates with solid coloured horses. The first is her right side, the second image, her left.
A lovely Palomino Frame Overo colt named Meteor. He has a lot of white on both hinds legs (the white goes up the front of the leg to the stifle) and this indicates there is probably another pinto gene such as Sabino or Tobiano, is present. Sand Wash Basin, Colorado
Kokomo, a Bay stallion by Picasso and a minimally marked Chestnut Frame Overo mare walking in front. Although they are muddy, the mare has solid legs and Kokomo has both white legs marked with white including a thin strip almost reaching his chest. Although he is heavily marked with white, like his sire, they both have solid coloured backs. Sand Wash Basin, Colorado
A very Minimally Marked Frame Overo named caballero. The other side is also solid. However, there is a white spot on this stallion’s tail evident by the light colour at the end. The facial marking (apron and pigmented lip) are good indicators of a Frame Overo. Sand Wash Basin, Colorado

Lethal White

The Frame Overo (Ff or Oo) trait is found on the equine chromosome #17 at the same locus (location on a chromosome) that controls EDNRB (Endothelin Receptor B) (Sponenberg, 20009). The change in the dinucleotide that occurs in Frame Overos changes an amino acid from isoleucine to lysine which disrupts the function of the EDNRB. In homozygous Frame Overo horses (Ff), the functional inability of Receptor Type B proteins (EDNRB) causes loss of gastric ganglia precursor cell migration and loss of melanocyte migration (Bailey & Brooks, 2013).The loss of function in EDNRB prevents the embryologic migration of:

  • Gastric ganglia precursor cells from migrating, which means a loss of enervation in the digestive tracts. No nerves ending exist in the colon of these horses and function is completely disrupted. Rarely the loss of EDNRB function results in an incomplete colon (ileocolonic aganglionosis). Foals with either gastric malformation die within a few days of birth and it cannot be surgically corrected.
  • Melanocyte migration means loss of pigment, resulting in white colouration.
In heterozygous horses, the presence of one “f” results in partial solid colour, but the digestive system is normal. In lethal white, the presence of two “ff” results in a pure white horse (no melanocyte migration) and a non-functional colon, or a blocked, atrophied, or dead-end colon. The loss of gastric enervation has a similar aetiology to Hirschsprung’s Disease in humans. Overo Lethal White Syndrome is found in Frame Overo horses as well as highly white calico overo, and frame blend overo (>94%) (Santschi, Vrotsos, Purdy & Mickelson, 2001)
Mingo X Picasso
©Nancy Roberts
©Nancy Roberts

Picasso X Fleck
 ©Danielle M. Williams
 ©Danielle M. Williams
 ©Danielle M. Williams

Here is the link for more information on the Lethal White Syndrome including a handy Punnett Square

References

Bailey, E., & Brooks, S. (2013). Horse Genetics (2nd ed.). Boston, Massachusetts: CABI.

Gower, J. (2016). Horse Color Explained: A Breeder’s Perspective. Brattleboro, Vermont: Echo Point Books & Media, Inc.

Kerson, N. (2015). What Color is that?  A quick guide to horse color identification: Nancy Kerson- Self Published

Santschi, E. M., Vrotsos, P. D., Purdy, A. K., & Mickelson, J. R. (2001). Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. Am J Vet Res, 62(1), 97-103.

Sponenberg, D. (2009). Equine Color Genetics (3rd ed.). Ames, Iowa: Wiley-Blackwell.

***A special thanks to Heather Robson & Nancy Kerson for identification and inspiration, respectively

About the Author & Photographers

AUTHOR & PHOTOGRAPHER

Dr. Meredith Hudes-Lowder, DNP, WHNP-BC, MSN, BSN, RNC, BS Biology
Meredith received a Bachelor of Science Degree from Binghamton University with an emphasis in ethology, conservation, and genetics. She received a Bachelor of Science in Nursing also from Binghamton and a Masters of Nursing in Perinatal/Women’s Health from Stony Brook University. She has a Doctorate of Nursing Practice from Stony Brook University. Her doctoral thesis was a research study on cervical cancer screening intervals. She was invited to present her research findings at the podium for the Nurse Practitioners in Women’s Health Annual Conference in New Orleans, October 2016. She is a member of several professional organisations and was inducted into Sigma Theta Tau- the Nursing Honor Society in 2007. She works at a busy medical practice in Manhattan as a Nurse Practitioner, specializing in the climacteric & menopause. She teaches Women’s Health to graduate students at Pace University in the clinical setting. When she is not busy taking care of “hot” women, Meredith can be found at the dojo practising Kobudo and Karate, performing pro-bono research for mustang advocacy, learning Korean, or playing her Lyon & Healy concert harp.


PHOTOGRAPHER
Karen McLain: Painter, artist, photographer

Karen McLain is a third generation Arizona native. Growing up in Arizona, she developed a deep appreciation for the outdoors, and for the rural and ranching lifestyle. Karen graduated from Arizona State University with a B.A. in Studio Art. She went on to pursue more traditional and realistic styles, and to create a style of her own. A number of commissioned works are accepted from collectors. The rest of the time, Karen can be found drawing or painting en plein air. These landscapes and life studies of wild horses are then developed into larger works in her studio.

McLain states: ”Painting from life not only reveals natures beauty first hand, but it also challenges me to focus and see clearly the light, form, and wonderful color present.  Time spent in the saddle, and painting en Plein air, results in an outlook that McLain describes as “Drawn from life, and inspired by life”, which is reflected in her work. See Karen’s “studio tour” here

END OF FRAME OVERO Horses
by Equus ferus Wild Horse Photography

The Tobiano Paints

 THE TOBIANO PAINTS

Disclaimer: The mustang photographs on this blog post are presented without genetic testing; we do not know the actual chromosomal make-up of the mustangs. We rely solely upon the horse’s phenotype, or how they appear physically: coat colour, white markings, eye color, mane, and tail colour.

Mammalian Pigmentation: 

The colors found in mammalian hair, skin, irises, and some internal organs is produced by the pigment melanin. Melanin appears as colored granules in these pigmented cells and occurs in two forms, eumelanin, and phaeomelanin. Eumelanin is responsible for brown and black colour, and phaeomelanin is responsible for reds and yellows (Bailey & Brooks, 2013).
Black tobiano (muddy) (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain
The absence of melanin will appear as white in mammals. The lack of color typically associated with Paint Horses is caused by the inability of these cells to produce the base colors from birth. The color loss results in large patches of white against a base coat of any colour (bay, chestnut, roan, grey, dun, champagne, silver dapple, palomino, brown, black, etc). Additionally, the white colour has pink skin beneath. 

Assorted tobiano horses (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain

There are other forms of white colouration in equines; for example gray or roan. Grey horse color is caused by the failure of melanocytes over time, so the hair starts normally pigmented but loses the ability to maintain the pigment so the horse eventually turns white(Sponenberg, 2009). Roan horses are roan from birth although they are often not recognizable until after the foal coat has shed. Roan horses typically retain the base color on their head, legs, mane, and tail. The skin beneath grey and roan horses is dark and these colors are not actual colours, but rather modifiers that act upon a base coat (Gower, 2016). 

Black tobiano demonstrating the “shield” (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus Wild Horse Photography ™© Karen McLain 
A tobiano horse may also be roan, appaloosa, sabinos, overo, or any other pattern as the tobiano pattern is not a mutually exclusive coat patterns.
Bay Roan tobiano   (Great Desert Basin, Utah) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Roan tobiano foal, palomino tobiano mare  (Great Desert Basin, Utah) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Equine chromosomes
The genes for four white coat patterns: roan (RN), sabinos (SB1), dominant white (W), and tobianos (TO) are located on the KIT gene.The KIT gene is responsible for sending instructions through cells that allow the cell to make specific proteins. The KIT proteins are found on the cell membrane where another protein called a “stem cell factor” binds to the KIT protein. When bound together, they activate the KIT protein, which in turn, activates other proteins within the cell. These proteins serve a variety of functions in mammalian cells such as growth, development, migration, and production of certain cell types such as interstitial gastrointestinal cells and melanocytes (Haase, Jude, Brooks, & Leeb, 2008).
Equine Chromosome #3
The KIT gene is located on the fourth chromosome at the 12 position and located very close is the ECA3 gene. The ECA3, or the third equine chromosome is the location of the chromosomal mutation responsible for tobianos. Although the KIT gene remains normal in these horses, the third chromosome has an area in the gene that has flipped. Approximately one-third the length of the chromosome is an area that is an exact mirror image in tobianos horses. Because the chromosomal inversion is adjacent to the KIT gene, it affects the KIT protein synthesis, and the cells cannot produce melanocytes- so the horse has areas of white. The test for tobianos examines the chromosome and looks for a ‘break’ (telomeric or centromeric) at the positions 13 and 21 on the third chromosome– this serves as an indication they separated and inverted during replication- the horse is genetically a tobianos (Bailey & Brooks, 2009).
The gene for tobiano horses is autosomal dominant. This means to be tobiano, a foal must have at least one tobiano parent, but they also may have two tobiano parents. If one parent is a tobiano, it does not matter what colour or pattern the other parent appears; the foal will be tobiano. If a horse matches the criteria for a tobiano, it is likely the horse has the genetic background of a tobiano, although there may be some mixing of other patterns (Gower, 2016). The patterns are not inherited exactly, however, the proportion of white to colour is inherited. In other words a horse with a lot of white will have offspring with a lot of white but this depends upon the other parent. Interestingly, the study by Woolf (1990) discovered male horses and those with chestnut coats have more white than female or bay horses. The researcher also noted that the inheritance of white leg markings and facial markings is multifactorial; there are many genes involved in the appearance of white markings (Woolf, 1990).

History:

Bay tobiano mare  (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
The Tobiano paint pattern was named for General Tobías from Brazil. The General brought the paint horses to Argentina in the mid-1800’s. Before their arrival, tobiano horses were rare and had been grouped with other spotted-type horses. After General Tobías’ arrival, they were renamed after the general and placed into a unique paint coat classification(Kerson, 2015; Sponenberg, 2009)
Tobiano Characteristics:
Bay tobiano mare (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
The tobiano is defined by several coat characteristics. As with all horses, unless genetically tested, we evaluate the coat pattern by the phenotype or the horses’ physical appearance. As a general rule, tobiano horses have the following characteristics (there are always exceptions to these rules):

  1. White cross the spine somewhere between the ears and the tail (Gower, 2016; Sponenberg, 2009)
  2. The body white appears to travel down in a vertical fashion (Gower, 2016)
  3. The edges of the white areas tend to be crisp and well-defined (Sponenberg, 2009)
  4. Legs are white and the edge of the socks/stockings is irregular (Gower, 2016; Sponenberg, 2009)
  5. Most tobiano have dark eyes although some tobiano horses have blue eyes  (Sponenberg, 2009)
  6.  Most tobianos have white areas within the mane and tail, this gives the appearance of a bicoloured tail, a trait usually seen only in tobiano horses. (Sponenberg, 2009)
  7. The predominantly solid coloured heads of tobianos are generally conservatively marked: thin blazes, simple stars (Sponenberg, 2009)

 Some tobianos have very little white

Black tobiano (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Minimally marked black tobiano stallion -note the bicoloured tail (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Bay tobiano stallion (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Black tobiano stallion (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Bay tobiano stallion (McCullough Peaks, Wyoming) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Some tobiano horses have very little base colour but they tend retain normally coloured heads even when extensively white.
Minimally marked light bay chestnut tobiano (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Light bay tobiano (note the minimal blaze) (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Extensively white black marked tobiano (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain
Some tobiano horses have marks within the white areas and there may be some bleeding of colour between the base colour and the white areas. The smaller spots in the white areas are called ink spots, bear tracks, cat’s paws. The areas of darker colour encroaching on the white areas are referred to as halos. There may also be some roaning at the edge of colour and white. This is a historical link between these markings and homozygosity. No genetic link has been found, however anecdotally, homozygous horses often present with these marking whilst heterozygous generally do not show these markings. 

Cat’s paws & halo effect (San Wash Basin, Colorado) © Equus ferus- Wild Horse Photography ™ © Karen McLain

Bay tobiano with the ‘halo’ effect (Black Hills Wild Horse Sanctuary, South Dakota) © Equus ferus- Wild Horse Photography ™ © Karen McLain
References
Bailey, E., & Brooks, S. (2009). Method for screening for a tobiano coat color genotype  #USPatent 8101354 B2.
Bailey, E., & Brooks, S. (2013). Horse Genetics (2nd ed.). Boston, Massachusetts: CABI.
Gower, J. (2016). Horse Color Explained: A Breeder’s Perspective. Brattleboro, Vermont: Echo Point Books & Media, Inc.
Haase, B., Jude, R., Brooks, S. A., & Leeb, T. (2008). An equine chromosome 3 inversion is associated with the tobiano spotting pattern in German horse breeds. 
Animal Genetics, 39(3), 306-309. doi:10.1111/j.1365-2052.2008.01715.x
Kerson, N. (2015). What Color is that?  A quick guide to horse color identification: Nancy Kerson- Self Published
Sponenberg, D. (2009). Equine Color Genetics (3rd ed.). Ames, Iowa: Wiley-Blackwell.
Woolf, C. M. (1990). Multifactorial inheritance of common white markings in the Arabian horse. J Hered, 81(4), 250-256.

A special thanks to Nancy Kerson for her brilliant book “What Color is that? A quick guide to horse color identification” and to the Black Hills Wild Horse Sanctuary. A worth sanctuary for wild horses.

by Equus ferus Wild Horse Photography

The Mustang Management Contraceptive Primer

MUSTANG MANAGEMENT CONTRACEPTIVE PRIMER 

This is not a debate on which is the best method of controlling wild horse numbers. These are simply the facts. It is clear science is far from perfect but research and observation can serve to give us an idea, a general sense of something which can compel us to look for more answers and continue research, preferably as humanely and as compassionately as possible. This is also not a debate as to whether mustangs should be classified as a native species in North America, returned native species, indigenous or invasive. They are here, with limited resources, and they are our responsibility.

————————————————————————–

Porcine Zona Pellucida (PZP):  The compound PZP, which is short for Porcina Zona Pellucida, is derived from sow ovaries. When the pigs are slaughtered for the meat industry, the excess tissue not used for the food industry is either discarded or utilized for non-consumption purposes. Some tissue used for research and others for the preparation of drugs. Heparin is a potent anticoagulant given to almost every patient who has had surgery followed by an overnight stay in the hospital, to prevent the formation of blood clots. Heparin is derived from pig intestines. Insulin, given to diabetics, was originally made from cow, pig, and even whale pancreases. Currently there are still some available that contain animal products, although there are genetically modified human insulins and insulin analogs that are not animal based (http://iddt.org/about/gm-vs-animal-insulin).


Pesticide Classification: The FDA classifies PZP as a pesticide simply because they do not have a category for contraception. Pesticides control the numbers of a populations be it insect or mammal, and because they can be quite destructive, pesticides are deemed as negative chemical compounds. PZPdoes not have any direct effect on any of the plants or animals other than the inoculated mares.

How it works: PZP works by stimulating the immune system of a mare to produce antibodies which migrate through the horse’s body to an oocyte (egg). When the mare ovulates, the antibodies immediately surround the egg, making it impenetrable to sperm. The egg cannot be fertilized and there is no foal. The reproductive behavior remains relatively normal, the mare goes into estrus and is covered by a stallion but there is no resulting offspring <!–[if supportFields]> ADDIN EN.CITE Barber200118(Barber, Lee, Steffens, Ard, & Fayrer-Hosken, 2001)181817Barber, M. R.Lee, S. M.Steffens, W. L.Ard, M.Fayrer-Hosken, R. A.Immunolocalization of zona pellucida antigens in the ovarian follicle of dogs, cats, horses and elephantsTheriogenologyTheriogenology1705-17175582001May0093-691XWOS:000168957100010<Go to ISI>://WOS:00016895710001010.1016/s0093-691x(01)00514-3<![endif]–>(Barber, Lee, Steffens, Ard, & Fayrer-Hosken, 2001)<!–[if supportFields]><![endif]–>.

Risks: PZP is not without risks. The currently long acting PZP-22 can last approximately 22 months. PZP is based on the immune system of the mares and this can cause variation in the efficacy and duration of the contraceptive effect. As in humans utilizing long term injectable contraception (Depo-Provera), the mare’s return to fertility is quite variable <!–[if supportFields]> ADDIN EN.CITE Kirkpatrick200924(Kirkpatrick et al., 2009)242417Kirkpatrick, J. F.Rowan, A.Lamberski, N.Wallace, R.Frank, K.Lyda, R.The practical side of immunocontraception: zona proteins and wildlifeJournal of Reproductive ImmunologyJournal of Reproductive Immunology151-157831-22009Dec0165-0378WOS:000273024800028<Go to ISI>://WOS:00027302480002810.1016/j.jri.2009.06.257<![endif]–>(Kirkpatrick et al., 2009)<!–[if supportFields]><![endif]–>. The reason PZP is not offered to humans is because the efficacy rate is not high enough.

“For contraceptive treatment to be an effective management tool, it usually needs to be reversible (Kirkpatrick & Turner 1991). A long term study of feral horses showed that PZP was reversible even when females were treated for several years (Kirkpatrick & Turner 2002). However some females appeared not to return to full fertility after long-term PZP treatment and similar side effects were seen with GNRH treatments in deer (e.g. Miller et al. 2000a). Consequently, most wildlife contraceptives are reversible, or have minimal impact after prolonged use.”  (Gray & Cameron, 2010).

Prolonged use has demonstrated that some mares will never return to fertility. Kirkpatrick, Liu, Turner, Naugle, and Keiper (1992)<!–[if supportFields]><![endif]–> found that three factors determine the return to normal reproductive function: the amount of PZP administered, the number of antibodies produced by the mare, and ovarian dysfunction. Earlier studies also demonstrated damage to ovaries although the PZP preparation was crude in the earlier stages of development <!–[if supportFields]> ADDIN EN.CITE Kirkpatrick199226(Kirkpatrick et al., 1992)262617Kirkpatrick, J. F.Liu, I. M. K.Turner, J. W.Naugle, R.Keiper, R.LONG-TERM EFFECTS OF PORCINE ZONAE-PELLUCIDAE IMMUNOCONTRACEPTION ON OVARIAN-FUNCTION IN FERAL HORSES (EQUUS-CABALLUS)Journal of Reproduction and FertilityJournal of Reproduction and Fertility437-4449421992Mar0022-4251WOS:A1992HR77000018<Go to ISI>://WOS:A1992HR77000018<![endif]–>(Kirkpatrick et al., 1992)<!–[if supportFields]><![endif]–>.

Abscesses at the injection sites have been reported but these are temporary, and heal without complications.

PZP and Tuberculosis: Finally, there were some rumours floating around social media that PZP can cause tuberculosis. Although this may sound like science-fiction or the nefarious work of people against keeping the horses wild, there is some truth. The original method of getting PZP into the animals involved piggy-backing the molecule on a carrier molecule or adjuvant. Adjuvants are not biologically active but their presence can trigger an immune response. It may result in a false positive antibody response for tuberculosis. The animal doesn’t have the disease, and many human vaccines work this way by stimulating the body to form antibodies to something not biologically active.  The original choice for the adjuvant was a mycobacterium- the mycobacteria family are known to cause tuberculosis and many other diseases. Because the PZP was attached to an inactive mycobacterium, in some animals it cause a false-positive tuberculosis antibody response. They changedthe adjuvant for the preparation of PZP so now there is no mycobacterium involved. Additionally, horses cannot contract or transmit tuberculosis <!–[if supportFields]> ADDIN EN.CITE  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endif]–>(Lyda, Hall, & Kirkpatrick, 2005)<!–[if supportFields]><![endif]–>.

GONACON: This method works by injecting mares with a synthetic (man-made) chemical compound called GonaCon. This compound acts against a hormone called gonadotropin releasing hormone (GnRH). In the reproductive cycle of mammals, GnRH is produced by the anterior pituitary gland. This gland controls reproduction by stimulating the release of the follicle stimulating hormone and the luteinizing hormone (and others). ConaCon works by stopping the production of GnRH and subsequently the luteinizing hormone and without LH, there is no ovulation, no corpus luteum, and therefore, no egg/offspring <!–[if supportFields]> ADDIN EN.CITE Speroff201230(Speroff & Fritz, 2012)30306Speroff, L.Fritz, M. Clinical Gynecologic Endocrinology and Infertility 8th2012New Yok Lippincott Williams & Wilkins<![endif]–>(Speroff & Fritz, 2012)<!–[if supportFields]><![endif]–>. Like PZP, GonaCon can result in prolonged infertility (Ransom, 2014). The tables below represent one study each- these data are only reflecting the results one study and may not have generalisability to the entire population. The general consensus amongst zoos and researchers is that PZP is 90% effective when administered correctly.

In a study by <!–[if supportFields]> ADDIN EN.CITE Ransom201429Jason I. Ransom et al. (2014)292917Ransom, Jason I.Powers, Jenny G.Garbe, Heidi M.Oehler Sr, Michael W.Nett, Terry M.Baker, Dan L.Behavior of feral horses in response to culling and GnRH immunocontraceptionApplied Animal Behaviour ScienceApplied Animal Behaviour Science81-92157Equus caballusFertility controlGonadotropin releasing hormoneSocial behaviorWild horseWildlife contraception20148//0168-1591http://www.sciencedirect.com/science/article/pii/S016815911400135Xhttp://dx.doi.org/10.1016/j.applanim.2014.05.002<![endif]–>Jason I. Ransom et al. (2014)<!–[if supportFields]><![endif]–>, the researchers found there were fewer behavioural differences in mares treated with GonaCon, compared to those treated with PZP. They modeled their GonaCon study after the PZP study and found fewer alterations in the wild mare’s behavior. GonaCon is still a recent addition to the world of wildlife contraception and has potential as a potential management tool for equids. It shows promise but the long-term data is still unavailable.  


GonaCon can be given to males because the GnRH stimulates testosterone production in males. However, studies of stags treated with GonaCon resulted in antler deformity and other negative consequences. “In conclusion, the GnRH vaccination in male rusa deer resulted in the increase in GnRH antibody titer, which negatively correlated with blood testosterone. The decrease in blood testosterone might be involved in the lower semen quality and poor antler development” (Phraluk, O. et al, 2015). There is potential for use in stallions but we need more research in this area.


Because GonaCon a works systemically, not targeting the reproductive tract as specifically as PZP, the potential for side effects increases. The closer to the intended target a medication or treatment is administered, the more effective, the lower the dose, and adverse drugs reaction are substantially decreased. The Global Library of Women’s Health states: “In non-reproductive tissues, GnRH has been reported to modulate neuronal migration, visual processing, digestive tract function, and immune T cell chemotaxis. Studies in endometrial, ovarian, and prostate tumor cell lines have implicated GnRH in mediating cell growth, angiogenesis, invasion, and metastasis.” (http://www.glowm.com/section_view/heading/Gonadotropin-releasing%2520Hormone%2520(GnRH)%2520and%2520the%2520GnRH%2520Receptor%2520(GnRHR)/item/284)
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Table 1. (Represents data from one study)
Infertility over three-years with equine contraception (Kilian et al., 2006).
Infertility after one year
Infertility after two years
Infertility after three years
Spay- Vac PZP
100%
80%
80%
GonaCon
94%
60%
53%
Copper IUD
80%
29%*
14%*
*The assumption is the IUD’s had been expelled in the mare who became pregnant

Table 2. (Represents data from another study)

Foaling rates at three horse management areas after PZP treatment  (Ransom, J.,et al, 2011).
Foaling Rates
Type of contraception
Treated
Untreated
Little Book Cliffs
6.6%
60.1%
PZP in liquid form requires annual boosters
McCullough
31.7%
75%
PZP in pelleted form- designed to last two years
Pryor Mountain
17.7%
62.8%
PZP in liquid form requires annual boosters
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Any time we begin to tamper with Mother Nature- it places us at risk. Treating mares with immunocontraception and/or Gonacon can have negative consequences on the familial structures of a highly social animal. Treating mares with these two compounds can result in mare giving birth to foal during time of limited resources. A study determined that there are differences in parturition times for mare treated compared with mares that were not treated. Foals born during more normal times for wild horses have a higher survival rate. <!–[if supportFields]> ADDIN EN.CITE Ransom201331(J. I. Ransom, Hobbs, & Bruemmer, 2013)313117Ransom, J. I.Hobbs, N. T.Bruemmer, J.Contraception can Lead to Trophic Asynchrony between Birth Pulse and ResourcesPlos OnePlos One812013Jan1932-6203WOS:000315211500043<Go to ISI>://WOS:000315211500043e5497210.1371/journal.pone.0054972<![endif]–>(J. I. Ransom, Hobbs, & Bruemmer, 2013)<!–[if supportFields]><![endif]–>.  

However, all negative consequences of injectable contraception pale in comparison to the disruption of the social structure during round-ups. Separation of mares from stallions and their offspring occurs during round-ups and culling. Family bands are broken up and the horses face the terrible loss of their freedom. A balance must be found and the benefits and the negative outcomes must be weighed. There is a chance a mare treated with the above methods, may never foal again- but that mare remains free. There is always the potential she may resume ovulation however, she is will not spend her life in a holding pen. A study by Turner, Liu, Flanagan, and Rutberg (2007) indicated one mare out of sixteen in the study, did not have a normal return to fertility. Is a chance of infertility worth the price of freedom?
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OVARECTOMY: This is removal of a mare’s ovaries. This method is irreversible, the mare will never breed again. Behaviorally, it reverts a mare to a non-breeding state. There is not a lot of data and/or research regarding this permanent method in the wild horse population which is why research proposals are being requested by government agencies The risks are the this surgical procedure are post-operative infection and possible abortion of a fetus if the mare is gravid at the time of the procedure.  Additionally there is the loss of that mare’s potential contribution to the genetic diversity of that herd management area.  This loss is not well defined and may vary based of the genetic variation in a herd management area. Mares should be monitored for three weeks post-operative (optimally), before being returned to the range to live out their lives. The upfront cost is high, but the end result is permanent. It has been proposed for mare over a certain age, selected by the currently proposed studies, as means to control the populations which would allow the mares to live free without foaling year after year (Speroff & Fritz, 2012, National Research Council, 2013).


CHEMICAL STERILIZATION/VASECTOMY/NEUTERING:  These methods, performed on stallions, are permanent means of limiting wild horse populations. In chemical sterilization, stallions have a solution injected into the testes which causes necrosis and eventual tissue death of the testes. It is painful and carries a high risk of infection but is very cost-effective (Zhanwei, 1989),  Orchiectomy (removal of testes: aka gelding/neutering) is another permanent method which removes the testes of a stallion. Like chemical sterilization, ‘gelding’ causes behavioral changes and the stallions become less aggressive, there is less fighting and they cannot reproduce. Vasectomy involves severing the vas deferens of a stallion so that the communication between the testes and the penis is removed. The sperm are not able to be passed through the urethra during copulation. Behavior remains the same because the testes are still present and producing testosterone. Infection rates are much lower in vasectomies, the procedure is less painful but it requires a delicate touch, it may not be 100% effective, and the horse must be anesthetized or sedated (Speroff & Fritz, 2012, National Research Council, 2013).

ROUND-UPS: This method involves gathering the horses by use of helicopters, men on horses, ATV, trucks, and bait trapping. The bait-trapping is the least likely to cause physical harm but none of these methods are without significant risks. Helicopter round-ups have the highest incidences of morbidity and mortality.  The horses are gathered, separated and either returned to the horse management area, or they are removed to a holding facility for potential adoption.

RESERVE DESIGN:  This method of mustang management has merit in a perfect world. The theory is to find a place for the horses to live. A place that has natural horse-predators (may prove to be difficult to find), natural barriers to prevent migration in/out of the area, and neighbours sympathetic to mustangs.  The area has to have sufficient food, water, shelter, and other necessities for survival year round. Funds for this preserve may be obtained through ‘eco-tourism’ and public education regarding the wild horses are included in this plan.  Reserve design is a wonderful idea but it does not have practical application. The land that would be needed is not available, at least not at this time, for the numbers necessary.  The monitoring of these herds and the management of these herds must be carried out as well and the necessary people to oversee each area. The goal of ‘reserve design’ is to be self-sufficient in which the wild horses achieve homoeostasis with regards to population growth. Because the predation is very low, and we cannot safely import predators, this will prove to be challenging. Incorporating natural predators to assist in controlling the wild horse population can have deleterious effects on the domestic population of horses and of livestock. Historically, once a predator begins to hunt within the domestic population, the end result usually has rather negative consequences for the predator.


SELF-REGULATION: This involves leaving the mustangs alone to establish population equilibrium without any interference. There is no scientific evidence that this methods works and history has shown us wild horses do not fare well with a hands-off approach. Unfortunately the resources the mustangs have within the management areas are limited and the horses will suffer in one way or another if left unmanaged. There are three factors that determine a population’s ability to grow. They are: available resources, predation, and disease. Many of the wild horses at Cold Creek starved to death or had to be humanely euthanized because resources became compromised.  The resources may be limited due to naturally occurring factors such as drought or fire, or they may face competition from livestock grazing on the same land. Regardless of the mechanism, reduced resources will cause competition, and result starvation or disease in the wild horse population. Occasionally a mountain lion will take a foal or an older/injured horse but cougars are not primary predators of the mustangs . Wolves generally do not live in the horse management areas with any regularity. Disease is a concern with any animal left in overcrowded situations. Chronic Wasting Disease is a disease that began in the mule deer population, and has spread to other cervids (herbivorous even-toed mammals in which the male carries antlers). The current deer populations are substantially larger than the available resources in the north-east United States, and this disease has now been identified in white-tailed deer of the Adirondack Mountains. Similar to Bovine Spongiform Encephalopathy (BSE), or Mad Cow Disease, this disease is affecting all cervids, not just the deer (Chronic Wasting Disease Alliance, 2016).  If the populations of wild horses were left alone, they would increase to the point of starvation and disease. It would only be a matter of time before a disease mutated in that population and spread to the domestic horse population with devastating consequences.

DECLARING THE MUSTANG “ENDANGERED”: This method is to first declare the mustang a ‘native wild species’ and then have it declared endangered- which may prove difficult. The mustang is the same species as domestic horses. They fall within the same genera: Equus and species: caballus. They have no genetic markers or any other characteristic that differentiate them from their domestic counterparts.  There has been proposed theories that they behave differently but this was not enough for the United States Fish and Wildlife to declare mustangs as a separate subspecies.  The wild horses are identical genetically, physiologically, and behaviorally to the horses in your paddock.  There are currently 40-50,000 presumably wild horses in captivity at BLM holding facilities. There are an estimated 20-40,000 living wild on horse management areas, and several thousand more domesticated mustangs living with people. These numbers alone are not sufficient for endangered species status, or even threatened species if USFW was willing to grant them subspecies status. 

Proponents of making mustangs endangered believe that once they achieve the endangered species status, the mustangs would be granted the ultimate protection. However, advocacy groups would no longer have a say in their conservation; they would be managed by Fish and Wildlife. The now ‘endangered’ mustangs may be moved to locations to protect their numbers and they may very well lose their freedom if they were to ever to gain protected status. Our descendants would not be able to see these ‘endangered mustangs’ living free; they would only see them in zoos and protected reserves.


The belief that mustangs are a separate species or a separate animal from domestic horses is the first hurdle to overcome with this method. However, that has proven to be impossible. They are not separate; they are the same species just as a miniature horse and a Clydesdale are the same species. They are horses that have returned to the wild and been wildly successful at surviving and reproducing.   

“Managing them to extinction” is a catch-phrase often used to describe the situation of the wild horses. Mustangs will never become extinct because they aren’t recognized as a separate sub-species of the modern horse. However, there is a very good chance our children and their descendants will never see a free roaming mustang, and that would be the greatest tragedy of all. Regardless of their origin, regardless of their heritage, the mustangs are our responsibility. We need science to save the mustangs, scientists with the necessary credentials and expertise in wildlife management, ecology, contraceptive experts, and equine ethology all working to establish the best and most humane method of managing wild horses. Each management area is unique and each management area needs its own method of achieving appropriate and healthy numbers. The phrase “managing them to eradication” is more accurate, less sensational rhetoric and implies the same message without any controversy regarding the species/subspecies status of the wild mustangs.  


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Meredith Hudes-Lowder is a Nurse Practitioner in Women’s Health and an expert on contraception. Additionally, she has a bachelor’s of biology with a concentration in environmental education.  She will graduate in May 2016 with a Doctorate of Nursing Practice. She runs the largest exclusively wild horse photography site on Facebook with Karen McLain- they have almost half a million fans. Bruce Lowder was consulted for this blog. He is a wildlife expert, naturalist, and worked for U.S. Fish and Game.
References:

Barber, M. R., Lee, S. M., Steffens, W. L., Ard, M., & Fayrer-Hosken, R. A. (2001). Immunolocalization of zona pellucida antigens in the ovarian follicle of dogs, cats, horses and elephants. Theriogenology, 55(8), 1705-1717. doi:10.1016/s0093-691x(01)00514-3
Gray, M. E., & Cameron, E. Z. (2010). Does contraceptive treatment in wildlife result in side effects? A review of quantitative and anecdotal evidence. Reproduction, 139(1), 45-55. doi:10.1530/rep-08-0456


Chronic Wasting Disease Alliance (2016). Webage URL http://www.cwd-info.org/index.php/fuseaction/about.main. Accessed 01/11/2016.

Killian, G., Diel, N., Miller, L., Rhyan, J, Thain, D. (2006). Long-Term Efficacy of Three Contraceptive Approaches for Population Control of Wild Horses. USDA National Wildlife Research Center – Staff Publications.

Kirkpatrick, J. F., Liu, I. M. K., Turner, J. W., Naugle, R., & Keiper, R. (1992). LONG-TERM EFFECTS OF PORCINE ZONAE-PELLUCIDAE IMMUNOCONTRACEPTION ON OVARIAN-FUNCTION IN FERAL HORSES (EQUUS-CABALLUS). Journal of Reproduction and Fertility, 94(2), 437-444.  Retrieved from ://WOS:A1992HR77000018
Kirkpatrick, J. F., Rowan, A., Lamberski, N., Wallace, R., Frank, K., & Lyda, R. (2009). The practical side of immunocontraception: zona proteins and wildlife. Journal of Reproductive Immunology, 83(1-2), 151-157. doi:10.1016/j.jri.2009.06.257
Lyda, R. O., Hall, J. R., & Kirkpatrick, J. F. (2005). A comparison of Freund’s Complete and Freund’s Modified Adjuvants used with a contraceptive vaccine in wild horses (Equus caballus). J Zoo Wildl Med, 36(4), 610-616. doi:10.1638/04104.1

National Research Council, (2013). Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward. PDF accessed 01/12/16: http://www.nap.edu/catalog/13511/using-science-to-improve-the-blm-wild-horse-and-burro-program.

Phraluk, Orasa; Wajjwalku, Worawidh; Siriaroonrat, Boripat; Booddee, Orawan; Thongtip, Nikorn. (2015). Effects of immunization against gonadotropin releasing hormone on reproductive functions in male rusa deer (Rusa timorensis). The Thai Journal of Veterinary Medicine 45.1   (Mar 2015): 1,3-10.
Ransom, J.,   Roelle, J.,  Cade, B., Coates-Markle, L., Kane, A., Ransom, Jason I., Roelle, James E., Cade, Brian S.,Coates-Markle, L., & Kane, A. (2011) Foaling Rates in Feral Horses Treated With the Immunocontraceptive Porcine Zona Pellucida. WILDLIFE SOCIETY BULLETIN.
Ransom, J. I., Hobbs, N. T., & Bruemmer, J. (2013). Contraception can Lead to Trophic Asynchrony between Birth Pulse and Resources. Plos One, 8(1). doi:10.1371/journal.pone.0054972
Ransom, J. I., Powers, J. G., Garbe, H. M., Oehler Sr, M. W., Nett, T. M., & Baker, D. L. (2014). Behavior of feral horses in response to culling and GnRH immunocontraception. Applied Animal Behaviour Science, 157, 81-92. doi:http://dx.doi.org/10.1016/j.applanim.2014.05.002
Speroff, L., & Fritz, M. (2012). Clinical Gynecologic Endocrinology and Infertility (8th ed.). New Yok: Lippincott Williams & Wilkins.
Turner, J. W., Liu, I. K. M., Flanagan, D. R., & Rutberg, A. T. (2007). Immunocontraception in wild horses: One inoculation provides two years of infertility. Journal of Wildlife Management, 71(2), 662-667. doi:10.2193/2005-779

Zhanwei, S. (1989). Chemical castration of horses and mules by injecting testis with iodine tincture. Journal of Liaoning Animal Husbandry and Veterinary Medicine.

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Other resources:

Barber, M. R., Lee, S. M., & Fayrer-Hosken, R. A. (1998). Staining patterns to the zona pellucida of the dog, cat, horse and elephant with porcine zona pellucida (pZP) antisera. Theriogenology, 49(1), 307-307. doi:10.1016/s0093-691x(98)90660-4
Barber, M. R., Lee, S. M., Steffens, W. L., Ard, M., & Fayrer-Hosken, R. A. (2001). 

Immunolocatiom of zona pellucida antigens in the ovarian follicle of dogs, cats, horses and elephants. Theriogenology, 55(8), 1705-1717. doi:10.1016/s0093-691x(01)00514-3


Berger, J. (1983). Induced abortion and social factors in wild horses. Nature, 303(5912), 59-61.  Retrieved from http://dx.doi.org/10.1038/303059a0

Bowling, A. T., & Touchberry, R. W. (1990). Parentage of Great Basin Feral Horses. The Journal of Wildlife Management, 54(3), 424-429. doi:10.2307/3809652

Duncan, P. (1982). Foal killing by stallions. Applied Animal Ethology, 8(6), 567-570. doi:http://dx.doi.org/10.1016/0304-3762(82)90221-8
Feh, C. (1990). Long-term paternity data in relation to different aspects of rank for camargue stallions, Equus caballus. Animal Behaviour, 40(5), 995-996. doi:http://dx.doi.org/10.1016/S0003-3472(05)81007-3

Feh, C., & Munkhtuya, B. (2008). Male infanticide and paternity analyses in a socially natural herd of Przewalski’s horses: sexual selection? Behav Processes, 78(3), 335-339. doi:10.1016/j.beproc.2007.12.009

Gray, M. E. (2009). An infanticide attempt by a free-roaming feral stallion (Equus caballus). Biol Lett, 5(1), 23-25. doi:10.1098/rsbl.2008.0571

Gray, M. E., & Cameron, E. Z. (2010). Does contraceptive treatment in wildlife result in side effects? A review of quantitative and anecdotal evidence. Reproduction, 139(1), 45-55. doi:10.1530/rep-08-0456
Gray, M. E., Thain, D. S., Cameron, E. Z., & Miller, L. A. (2010). Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations. Wildlife Research, 37(6), 475-481. doi:10.1071/wr09175
Jordana, J., Pares, P. M., & Sanchez, A. (1995). ANALYSIS OF GENETIC-RELATIONSHIPS IN HORSE BREEDS. Journal of Equine Veterinary Science, 15(7), 320-328. doi:10.1016/s0737-0806(06)81738-7
Kavar, T., & Dovc, P. (2008). Domestication of the horse: Genetic relationships between domestic and wild horses. Livestock Science, 116(1-3), 1-14. doi:10.1016/j.livsci.2008.03.002

Kirkpatrick, J. F., Liu, I. M. K., Turner, J. W., Naugle, R., & Keiper, R. (1992). LONG-TERM EFFECTS OF PORCINE ZONAE-PELLUCIDAE IMMUNOCONTRACEPTION ON OVARIAN-FUNCTION IN FERAL HORSES (EQUUS-CABALLUS). Journal of Reproduction and Fertility, 94(2), 437-444.  Retrieved from ://WOS:A1992HR77000018

Kirkpatrick, J. F., Rowan, A., Lamberski, N., Wallace, R., Frank, K., & Lyda, R. (2009). The practical side of immunocontraception: zona proteins and wildlife. Journal of Reproductive Immunology, 83(1-2), 151-157. doi:10.1016/j.jri.2009.06.257

Kirkpatrick, J. F., & Turner, A. (2002). Reversibility of action and safety during pregnancy of immunization against porcine zona pellucida in wild mares (Equus caballus). Reproduction (Cambridge, England) Supplement, 60, 197-202.  Retrieved from http://europepmc.org/abstract/MED/12220160

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Linklater, W. L., Cameron, E. Z., Stafford, K. J., & Minot, E. O. (2013). Removal experiments indicate that subordinate stallions are not helpers. Behav Processes, 94, 1-4. doi:http://dx.doi.org/10.1016/j.beproc.2013.02.005

Lyda, R. O., Hall, J. R., & Kirkpatrick, J. F. (2005). A comparison of Freund’s Complete and Freund’s Modified Adjuvants used with a contraceptive vaccine in wild horses (Equus caballus). J Zoo Wildl Med, 36(4), 610-616. doi:10.1638/04104.1

Madosky, J. M., Rubenstein, D. I., Howard, J. J., & Stuska, S. (2010). The effects of immunocontraception on harem fidelity in a feral horse (Equus caballus) population. Applied Animal Behaviour Science, 128(1–4), 50-56. doi:http://dx.doi.org/10.1016/j.applanim.2010.09.013

Mask, T. A., Schoenecker, K. A., Kane, A. J., Ransom, J. I., & Bruemmer, J. E. (2015). Serum antibody immunoreactivity to equine zona protein after SpayVac vaccination. Theriogenology, 84(2), 261-267. doi:10.1016/j.theriogenology.2015.03.012

Massei, G., & Cowan, D. (2014). Fertility control to mitigate human-wildlife conflicts: a review. Wildlife Research, 41(1), 1-21. doi:10.1071/wr13141

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Pluhacek, J., & Bartos, L. (2000). Male infanticide in captive plains zebra, Equus burchelli. Anim Behav, 59(4), 689-694. doi:10.1006/anbe.1999.1371

Ransom, J. I., Hobbs, N. T., & Bruemmer, J. (2013). Contraception can Lead to Trophic Asynchrony between Birth Pulse and Resources. Plos One, 8(1). doi:10.1371/journal.pone.0054972

Ransom, J. I., Powers, J. G., Garbe, H. M., Oehler Sr, M. W., Nett, T. M., & Baker, D. L. (2014). Behavior of feral horses in response to culling and GnRH immunocontraception. Applied Animal Behaviour Science, 157, 81-92. doi:http://dx.doi.org/10.1016/j.applanim.2014.05.002

Schulman, M. L., Botha, A. E., Muenscher, S. B., Annandale, C. H., Guthrie, A. J., & Bertschinger, H. J. (2013). Reversibility of the effects of GnRH-vaccination used to suppress reproductive function in mares. Equine Veterinary Journal, 45(1), 111-113. doi:10.1111/j.2042-3306.2012.00577.x

Speroff, L., & Fritz, M. (2012). Clinical Gynecologic Endocrinology and Infertility (8th ed.). New Yok: Lippincott Williams & Wilkins.

Turner, J. W., Liu, I. K. M., Flanagan, D. R., & Rutberg, A. T. (2007). Immunocontraception in wild horses: One inoculation provides two years of infertility. Journal of Wildlife Management, 71(2), 662-667. doi:10.2193/2005-779