The Appaloosa’s unique spotted coat patterns and distinct markings set them apart from other horses and are among the breed’s most defining traits. Appaloosas are also known for their athleticism and versatility, excelling in a variety of disciplines including racing, dressage, barrel racing, trail riding, cutting and more. Appaloosas’ stunning appearances are a result of various genes that determine the distribution and expression of color and spots. Understanding how these genes work can help you make informed breeding choices, allowing you to select for the exact pattern you want in your next foal.
Genetically, almost all appaloosas have a spotted coat caused by the leopard complex (LP) gene mutation. However, the number of LP alleles and the presence of additional “pattern modifier” genes can have a significant impact on the final appearance of an appaloosa’s pattern.
Generally, the more LP alleles an animal carries, the more extensive and distinct the spotted pattern will be. In general, a horse that has at least two LP alleles and no other pattern modifier genes will display the classic leopard complex phenotype of white with dark base colored spots in a fairly even distribution around the body. This type of pattern is reminiscent of a dalmation or a fawn and may exhibit varnish marks or roaning.
If a horse has one LP allele and no other pattern modifier genes, it will have minimal or no noticeable spotted pattern. These horses are sometimes referred to as snowcaps or blankets and will usually have a light or medium color base with only a few darker points, or “varnish marks” located on the flank, elbow, face and hindquarters. These horses are often described as marble or roan and can develop lighter areas of varying degree on the face, legs, stifle and hip point, as well as on the neck and head.
As a side effect of the leopard complex gene, appaloosas tend to have mottled skin. This is seen most notably in the soft areas of the face and muzzle where there is a light or pink color with a dark spot in the center. This is not always evident in young foals and can fade over time.
Interestingly, the LP gene also affects eye health in some horses. Those with the LP gene that carry two LP alleles and no other modifying genes are at an increased risk for developing Equine Recurrent Uveitis (ERU), a chronic intraocular inflammation that can cause blindness in horses. A recent study using genome-wide association techniques has linked markers close to LP on ECA1 with a higher risk for developing ERU in appaloosas.
Although the Leopard complex gene has been analyzed and mapped, there is likely still much to be discovered about appaloosa patterns. It seems that other phenotypes and pattern modifiers are involved in the final appearance of a leopard complex spotted horse, and there are probably more genes that interact with the leopard complex gene to produce more complex patterned phenotypes than we know about currently.