EQUINE HEALTH so it is possible to get a relatively economical overview of what your horse’s genetic status is on those diseases,” she said. “Owners can then select mates to breed away from a trait or decide it is not worth the risk of passing on the genetic condition.” It is important to understand how dominant and recessive traits can work and benefit or harm a foal, because this will influence breeding decisions. “If your horse has a recessive trait you’d want to breed to a horse that does not carry that trait, to avoid any chance of having an affected foal,” Valberg said. “If your horse has a dominant trait, however, and is heterozygous (one normal gene, along with the gene for the genetic disease), no matter what horse you breed to, there is a 50 percent chance that the offspring will be affected.” This could lead to the heartbreak of producing an affected foal, whether it’s your own or a foal from someone else’s mare bred to your stallion. “If you have an affected foal and are trying to sell it later, this will affect its
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value if genetic testing is done as part of a pre-purchase exam,” said Valberg. “If you are purchasing a horse and wonder if it might have an underlying genetic disorder, it’s wise to find out—since this may affect the horse’s ability to perform. If you have done genetic testing on animals you are selling, you have a duty to disclose the results of those tests.” Dr. Carrie Finno, Assistant Professor and Researcher, Population Health and Reproduction, UC-Davis, does genetic research looking for mutations in horses. “It’s important for new horse owners to understand, especially in the Quarter Horse world, that even if you are not considering breeding your animal, you should do the 5-panel test as part of a pre-purchase exam because a lot of the muscle diseases can be performance-limiting. They can be managed, but you should know the genetic status of a horse before you purchase, because this is a lifelong management issue. With genetic diseases, nothing is curative, so all we can do is use this knowledge to manage those horses appropri-
ately. It’s best to go into this with eyes wide open, rather than find out after the fact that the very nice horse you’ve purchased has a problem. Some people don’t do the tests and go ahead and buy the horse, and later have problems.” There are many new horse owners who buy horses to show, and may not understand the importance of testing. They may not be familiar with some of the genetic diseases that old-timers have learned about, sometimes the hard way. “Someone could buy a horse and not know what questions to ask, like whether it has been tested,” said Dr. Gary Magdesian of the School of Veterinary Medicine at UC-Davis. “They might buy a horse that has a disease they didn’t know about. Ask for test results (or do the test) for any horse you are purchasing, so you know what you are getting into. “Testing provides knowledge, and knowledge is power,” he said. “There is a lot to learn, and most horse owners try to learn all they can about their horses, so they can make the best decisions regarding their care and breeding.”
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