Genetic testing is becoming more popular with equine organizations as we attempt to decrease the number of genetic diseases. Dr. Carrie Finno from UC Davis and Dr. Molly McCue from Minnesota talked about equine genetic diseases and testing at the AAEP convention. The cancer called squamous cell carcinoma is a common disease affecting Belgians and Haflingers that typically occurs with exposure to UV light. Lesions commonly develop at junctions like the eyes, lips and prepuce, and there is a test that breeders can use before breeding to determine if a horse is susceptible. Another genetic disease is immune-mediated myositis, which is a disease that causes rapid muscle loss in young quarter horses after exposure to infection or vaccination of certain diseases. A test is available to determine which quarter horses might be susceptible to immune-mediated myositis.
Another common genetic syndrome in quarter horses, Belgians, and Percherons is one form of tying up and this is polysaccharide storage myopathy, or PSSM. It occurs in a least 30 breeds so if you plan to breed or even buy a horse, it might be a good idea to test for this disease. Another form of tying up is due to type 2 PSSM but there is no genetic test for it and a muscle biopsy is required for diagnosis.
Another disease that may be genetic is equine asthma, previously called heaves. This disease may be related to multiple genes, but no test is available at this point.
The American Quarter Horse Association has taken the lead in genetic testing so it may appear that quarter horses have more genetic diseases than other horses, but that is not true. The large number of quarter horse tests available that exist are because the quarter horse folks have been more aggressive at testing, which is a good thing.