The Horse

OCT 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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Inquiries to: 859/276-6726 E-Mail: News@TheHorse.com ERICA LARSON, News Editor @TH_EricaLarson 10 October 2018 The Horse | TheHorse.com Myosin heavy chain 1 (MYH1), a gene respon- sible for producing—or encoding—the myosin protein in muscle tissue, is occasionally passed down to offspring in a mutated form. It's this mutated form that Carrie Finno, DVM, PhD, Dipl. ACVIM, of the University of California, Davis; Stephanie J. Valberg, DVM, PhD, Dipl. ACVIM, ACVSMR, of Michigan State University, in East Lansing; and colleagues recently linked to IMM development. Fast-contracting muscle cells express the myosin protein to enable muscle contractions, and MYH1 is one of several genes that encode myosin. Like all genes, MYH1 is made up of many thousands of base pairs, which contain a code for specific amino acids that create unique proteins. A single base pair in MYH1 dif- fered between healthy horses and those with IMM. Affected horses experi- ence rapid, widespread wast- ing of the gluteal and epaxial muscles (the latter run along either side of the spine); generalized muscle stiffness; and lethargy. These issues often arise following certain infections or vaccinations. Further, the team devel- oped a genetic screening test to check for the MYH1 mutation. "This genetic test will provide a significant advance in our ability to diagnose IMM," Finno said. "Pre- viously, the only way to diagnose IMM was to take (and evaluate) biopsies of specific muscles early in the course of developing muscle atrophy (wasting). Between atrophy episodes, there was no indication a horse was susceptible to this condition." Finno and Valberg recom- mend testing Quarter Horses to find out if they carry two copies (one from each parent) of the mutant gene, a single copy (from one par- ent), or none. "Horses with two copies of the mutation (My/My) are more severely affected," Finno said. "Both homozy- gous (My/My) and heterozy- gous (N/My) horses should be monitored closely for any evidence of muscle atrophy following an infection or vaccination." Valberg added, "This genetic test should also be used for horses that have had episodes of 'tying-up' that are not associated with exercise, because we see horses with this mutation develop quite severe muscle damage without necessarily showing atrophy." Learn more about IMM and the researchers' findings at TheHorse.com/159656. —Christa Lesté-Lasserre, MA A genetic mutation is to blame for immune- mediated myositis (IMM), a sometimes- fatal disease in Quarter Horses that the veterinary community has been striving to better understand. The researchers behind the discov- ery have also created a genetic screening test, which allows for easier identification of the dis- ease that causes horses to go from muscled and healthy to wasting away in a matter of days. Researchers Pinpoint Mutation Behind IMM Horses with IMM experience rapid, widespread wasting of the gluteal and epaxial muscles; generalized muscle stiffness; and lethargy. ISTOCK.COM NEWSFRONT Bone Scans Lack Accuracy in Hoof, Poor Performance Exams In a pair of recent studies, researchers determined that bone scans are best used in combination with other diagnostic and imaging modalities when used to examine poor performance and hoof issues. In one study researchers found that bone scans yielded a high proportion of false-negative and incidental findings in poor performance exams, leading them to conclude that bone scans used for screening for injury might not lead to a full—and correct—diagnosis. In the other study they found that while bone scans provide practitioners with infor- mation about some hoof injuries related to bone or soft-tissue-to-bone connections, they might not reveal other sources of foot pain. "I see limited value in whole-body screening of sports and leisure horses, but targeted examinations can be useful in some clinical situations," said Sue Dyson, VetMB, PhD, DEO, Dipl. ECVSMR, FRCVS, of the Animal Health Trust, in England. "Image quality and correct image interpretation are crucial." Structural Changes in Senior Horse Hearts A gray-speckle tracking ultrasound technique is helping scientists better understand how horses' hearts age. They detected significant heart structure differences between older and younger horses, mainly in the left ventricle, and a reduced capacity to con- tract. These differences were visible starting at around age 15. But, "we need much more information about what is normal in the older heart and what is perhaps pathological (relating to, amounting to, causing, or caused by a physical problem)," said Heidrun Gehlen, PhD, Dipl. ECEIM, of Freie Universitat, in Berlin. STUDY SHORTS

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