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HYPP is an autosomal dominant trait disorder. This is an important concept to understand because it means this disorder can occur in both males and females, and only one copy of the gene is required to produce disease. Therefore, both homozygous (have two identical alleles of a gene; HH) positive and heterozygous (have two different alleles of a gene; NH) horses will be affected. Only homozygous negative (NN) horses are not affected by HYPP. Because HYPP is a dominant genetic disorder, any other horse can potentially pick up the disorder when intermixing occurs. This trait is inherited from generation to generation with equal frequency, which means it does not skip generations nor does it get diluted. The current genetic test is considered 100 percent accurate for the mutation that causes HYPP. Although muscle weakness is the common characteristic of HYPP, clinical signs among horses carrying the genetic mutation may range from asymptomatic to daily muscle twitches and weakness. Some horses show signs following stressful situations, anesthesia or heavy sedation. In most cases, clinical episodes begin with a brief period of tightness or tension in the muscles. This may be followed by sweating and muscle twitches. Attempts, on the horse’s part, to move may only escalate the muscle tremors. Heart rates and respiratory rates may be elevated and horses may appear anxious yet remain bright and alert. Horses undergoing severe attacks may progress to weakness with swaying, staggering, dog sitting or recumbency within a few minutes. So, can a Half-Arabian carry the HYPP gene? If it has ancestry from affected Quarter Horse linage, then it is certainly possible. Because the HYPP gene will never be diluted across generations, close inspection of your Quarter Horse lines is warranted. If you are in doubt, or have Quarter Horse linage that you

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Issue 2. 2019

A horse exhibiting hair loss symptoms of HERDA. The deep layers of the skin are weak and thin, thus separating and tearing easily.

You cannot currently cure a genetic disease. However, you can treat the clinical signs, identify the disease via DNA testing, and avoid spreading the disease by removing affected individuals from breeding programs. Therefore, much of the equine genetic research is focused on identifying gene mutations that cause particular diseases and developing tests for them. n

do not know, the cost for submitting a mane or tail hair sample to a licensed laboratory for DNA testing to identify the specific genetic mutation is minimal compared to the potential chances of producing a foal with HYPP or purchasing a horse with the disorder. n n n The next genetic disorder is Hereditary Equine Regional Dermal Asthenia or HERDA. This is a rare condition occurring in some Quarter Horse bloodlines and related crosses. Researchers at Mississippi State University and Cornell University believe that the origin of this disorder may be Poco Bueno’s sire line. In affected horses, the deep layers of the skin are weak and thin, thus separating and tearing easily. The signs are most prominent along the areas under the saddle. Wounds along these areas are slow to heal and often leave permanent scars. The genetic defect occurs in the collagen that holds the skin in place. Signs typically appear between one and one and a half years of age, and may be particularly noticeable if the horse is regularly ridden. The clinical signs can range for mild,

Profile for Arabian Horse Association

Arabian Horse Life Magazine; mini issue 2 2019  

The Arabian Horse Association's (AHA) member magazine, Arabian Horse Life (AHL) is due to hit mailboxes the last week of April. Distributed...

Arabian Horse Life Magazine; mini issue 2 2019  

The Arabian Horse Association's (AHA) member magazine, Arabian Horse Life (AHL) is due to hit mailboxes the last week of April. Distributed...