One of the joys of spending time around horses is being able to appreciate their beauty. These dignified and charismatic equines display a broad palette of color and patterns. Some coat pigmentation variations, such as those found on brindle horses, are unusual and visually striking.
Brindle is a rare color pattern occurring on a variety of horse breeds. The brindle pattern appears as colored blotches or vertical streaks with a rougher texture than the rest of the horses’ coats. Brindle patterning usually results from genetic inheritance or abnormal embryo development.
You don’t need to be an equestrian to find the appearance of brindle horses mesmerizing. The reasons for the unique brindle patterning are equally intriguing. Let’s delve into brindle horses, horse breeds, and the genetic and embryonic processes responsible for this stunning streaked pigmentation anomaly.
What Are Brindle Horses?
Brindle horses get their name from the distinctive color pattern on their coats. This highly unusual color pattern is not limited to specific horse breeds.
There are three types of brindle horses, each categorized according to how they got their markings:
- inheritable,
- chimera,
- indeterminate.
Inheritable brindle horses get their unusual coat patterning from their parents. These horses inherit a genetic mutation that causes the brindle trait. In general, the color patterns on inheritable brindle horses are subtler and less distinct than the markings found on chimeras and indeterminates.
Chimeras have brindle markings due to abnormal embryo development rather than genetic inheritance. The color patterns on chimera horses contrast more dramatically with the rest of their coat when compared with inheritable brindle horses.
Indeterminate brindle horses exhibit coat markings that are reminiscent of the patterning on inheritable and chimera brindles. The brindle color pattern on indeterminate horses appears randomly and for unknown reasons. Indeterminate brindle horses display color markings whose boldness is comparable to the color patterning on chimeras.
Due to their rarity, foals with brindle markings are sought after and demand a premium price. Depending on the breed, brindle foals cost an average of $2500 to $5000.
How Does The Brindle Pattern Look And Feel?
The brindle pattern is composed of unmistakable, bold, vertical streaks or blotches on a horse’s coat. These markings are hairs with different pigmentation from the rest of the animal’s coat. Depending on their configuration, brindle color patterns give horses’ coats a marbled or paint-splattered appearance.
The color of brindle patterning is unique to individual horses but is usually a shade of light brown, black, or white (roan). The markings are usually distributed as streaks down the length of the horse’s body. In other instances, the brindle pattern looks like paint or mud splashes concentrated in a small area of the horse’s coat.
In addition to being a different color, the hairs constituting the brindle markings have a different texture to the rest of the horse’s coat. The brindle pattern hairs are slightly rough and wavy, and they are also longer and stand higher than the non-brindle coat hairs.
Brindle markings undergo seasonal changes. In winter, brindle horses have a longer, thicker coat that partially obscures the color pattern making it less distinctly visible. The brindle pattern is at its boldest and most striking in summer when the horses have thinner, shorter coats.
Which Breeds Are Brindle Horses?
The brindle color pattern is not limited to particular horse breeds. However, while all horse breeds have the potential to display brindle markings, the patterning occurs more frequently on certain horses than others. The horse breeds most commonly exhibiting the brindle pattern are:
- quarter horses,
- draft horses,
- ponies,
- American Paint horses.
Other horse breeds exhibiting this rare pattern (though with less frequency) include mustangs, thoroughbreds, and Arabians.
So, how do these horse breeds develop the brindle color pattern? As we’re about to see, it’s all about genes and embryos.
Brindle Horses: Inheritance Of A Genetic Mutation
Brindle horses usually inherit their unique patterning from one or both of their parents. For this reason, these equines are sometimes known as inheritable brindle horses.
The brindle trait in inheritable horses is generally limited to rougher hair texture and muted to barely visible color markings. Indeed, the color patterning on some inheritable brindles might go unnoticed by an unschooled observer!
The science is somewhat complicated, but here is a simplified explanation of the genetic processes involved.
Brindle Pattern Genetics
Inheritance of a gene mutation responsible for coat hair texture and pigmentation is usually the cause of brindle patterning on horses.
The mutation is primarily inherited through the X chromosome (which are DNA strands in cell nuclei). Female horses have two X chromosomes, which means they are more likely to pass the brindle trait to their offspring than stallions (who have a single X chromosome).
The brindle pattern is associated with an allele called Brindle1 or BR1 (the allele for non-brindle or normal coat color and texture is indicated as N). If a mare or stallion has the BR1 allele, some or all of its offspring will be brindle horses.
Every gene is composed of two alleles (gene variants), with one allele inherited from the male parent and the other received from the mother. The specific combination of the alleles is called the genotype, which is linked to the expression of particular traits, like coat hair texture and color.
Horse Breeding And Inheritance Of The Brindle Genotype
So, because male horses have one X chromosome, they can either have an N or BR1 allele that codes the proteins for their coat hair. Stallions with the BR1 allele usually do not have the brindle color pattern (and their tail and mane hair is often sparse) but they pass the brindle trait to 100% of their offspring.
In contrast, female horses can have two allele combinations (genotypes) for brindle coat texture and patterning traits (due to their two X chromosomes). Mares can either be BR1/BR1, N/BR1, or N/N.
A mare with the N/BR1 genotype will present the brindle color pattern. In general, 50% of the foals will be brindle horses, and 50% will not display this unique coat trait.
Female horses with the BR1/BR1 genotype are not brindle and typically have thin manes and tails. However, these mares pass the bridle trait to all their offspring.
Of course, the inheritance of the brindle trait also depends on the combination of the parental genes. For instance, the brindle patterning is generally more starkly visible when foals inherit the BR1 allele from both their parents.
You can get horses tested to check if they have the brindle genotype. Institutions like the University of California Davis Veterinary Genetics Laboratory offer testing for the BR1 allele. The UC Davis Lab test costs $25, and the turnaround time for receiving results is about two weeks.
Chimera Brindle Horses: Abnormal Embryo Development
A type of abnormal embryo development called chimerism is another cause of the brindle color pattern found on horses.
This extremely rare abnormality occurs when two non-identical twin zygotes (fertilized embryos) fuse into a single embryo during the nascent stage of pregnancy. The conjoined zygotes are encoded with different DNA and form a new individual fetus carrying both sets of genetic instructions.
In the case of chimera brindle horses, the trait occurs spontaneously during a mare’s early pregnancy and is non-heritable. Chimera foals might display the brindle patterning even though neither parent had the BR1 genotype!
It is intriguing and worth noting that the brindle patterning on chimeras is dramatically bolder than on horses that inherit the trait. Chimera horses’ brindle markings also cover a higher percentage of their bodies when compared with their heritable cousins.
Indeterminate Brindle Horses
The third brindle horse type is called indeterminate. These horses exhibit the brindle trait randomly and not because of genetic inheritance or chimerism. For this reason, some might argue that indeterminate horses are not true brindles. Nevertheless, these horses resemble inheritable and chimera brindles, so they are still included in the brindle horse category.
The reason for indeterminate brindle patterning is unknown. However, the phenomenon may be due to phenotypic expression (an observable trait in an individual organism resulting from a genotype or latent genetic potential expressed in response to living conditions or other external factors).
Like chimeras, the color patterning on indeterminate brindle horses is noticeably bolder and more visually striking than the markings on inheritable brindle horses. However, the brindle markings on indeterminate horses are usually more localized and less expansive than one finds on chimeras.
Seasonal Changes In Brindle Color Patterns
The color pattern on brindle horses looks different depending on the season.
Brindle markings become less visible when obscured by the thicker, longer coat that horses grow in winter. When horses shed their winter coats, the markings become more noticeable because the surrounding hair is shorter and less dense.
The color patterns on chimeras and indeterminate brindle horses are at their brightest and most beautiful in the summer months.
Horse breeders observe that the patterning on inheritable brindle horses looks most attractive in late fall.
Conclusion
Brindle horses boast a rare coat patterning. The brindle pattern is not unique to specific breeds of horses. This beautiful coat marking is usually composed of vertical streaks or patches of hair that have a different color and texture to the animal’s other coat hairs. Brindle markings vary in color from light to dark brown, black, and white.
The brindle color pattern is usually the result of genetic inheritance. Chimeric embryo development is another (less prevalent) cause of the brindle patterning on horses (called chimeras). Some horses (called indeterminate brindles) display brindle-like markings for unknown reasons. Chimera and indeterminate horses have the most visually-striking brindle color patterns.
Resources
https://vgl.ucdavis.edu/test/brindle-1-horse
https://justabrindlehorse.com/brindle-horses/brindle-coats/
