UC Davis

Equine veterinary genetic research has contributed significantly to the veterinary community, horse owners and breeders, animal welfare, and breed longevity. The discovery of causative mutations for inherited equine diseases allows veterinarians to recognize the clinical signs of disease, achieve definitive diagnoses via genetic testing, and make recommendations based on a patient’s breed or lineage. Owners and breeders benefit from these genetic discoveries, as they are not only offered more comprehensive veterinary care, but are also given the tools to test their horses for disease status in order to avoid breeding affected animals. Some inherited diseases in equines are fatal, so preventing transmission is highly critical for animal welfare as well as the cost of breeding and pregnancy. In Chapter 1 of this thesis, we report the causative genetic mutation for Equine Juvenile Spinocerebellar Ataxia (EJSCA), a novel, fatal autosomal recessive disease in young American Quarter Horse (AQH) foals. This study includes the functional validation of this variant and EJSCA allele and carrier frequencies. This new genetic test adds to the six genetic tests already available in this breed. Allele frequency studies allow researchers to estimate the genetic disease alleles within populations, which is important to monitor over time and especially when novel mutations are discovered. These studies give the veterinary community, breeders, and breed associations a clear picture of the risk an inherited disease poses because they highlight the temporal response to genetic test availability, any potential gaps in community education, and the prevalence of often devastating novel diseases. This allows breeders to make informed decisions about potential pairings and helps prevent unnecessary suffering. The persistence of disease alleles is harmful to breed longevity, since the greater the number of individuals with a disease variant, the more likely that allele will be passed onto offspring. In Chapter 2 of this thesis, we report the allele, carrier, and affected frequencies of seven critical diseases within the AQH breed, including EJSCA, in a randomly selected cohort and seven top performing cohorts of AQHs registered with the American Quarter Horse Association.