In April, UC Davis discovered a genetic disease unique to the American Quarter Horse breed. News yesterday of foals affected by the disease sired by the upcoming Metallic Cat son, Taggline has spurred social media into discussions about the disease.
“We hoped to have our own tests in hand to share the knowledge of Taggline’s carrier status of the newest testable disease,” wrote Taggline’s owner in a Facebook post. “We were made aware of this situation Tuesday and ordered our own test to furnish to the public this week with education on this disorder.”
The news, while concerning for many who breed Quarter Horses, has been met with appreciation by many in the horse community.
“Kudos to you for being proactive and educational. As long as we test our mares we can make appropriate decisions and this in no way should keep anyone with a n/n mare from choosing your stallion,” wrote on Facebook user.
“Thank you so much for educating the public and giving out this information! Obviously I’m among many who have never heard of this, and I appreciate any facts that are being put out,” wrote another.
Equine Juvenile Spinocerebellar Ataxia (EJSCA) is a genetic neurologic disease causing ataxia in American Quarter Horses. The variant responsible for this disease was identified by Dr. Carrie Finno and her team at UC Davis. Their scientific paper on the findings is in progress.
Dr. Finno discovered that affected foals develop incoordination between 1 and 4 weeks of age, with hind limbs usually more affected than the front.
As the disease progresses, foals turn their hind limbs to one side while keeping their front limbs planted, appearing to walk sideways. Within days, they can’t stand without help and must be euthanized.
EJSCA is inherited as an autosomal recessive trait. Genetic testing can identify carrier horses, and breeding two carriers has a 25 percent chance of producing an affected foal.
The American Quarter Horse Association has not yet published any information on this new genetic disease.
AQHA began requiring genetic testing for all registered breeding stallions in 2015. The five-panel test screens for genetic diseases that are caused by single DNA mutations, including: Glycogen branching enzyme deficiency (GBED), Hereditary equine regional dermal asthenia (HERDA), Hyperkalemic periodic paralysis (HYPP), Malignant hyperthermia (MH), and Polysaccharide storage myopathy type 1 (PSSM1).
The American Quarter Horse Association (AQHA) added a sixth test to its genetic health panel in 2023 for Myosin-Heavy Chain Myopathy (MYHM).