Muscle Disorders in Warmbloods Easily Diagnosed through Biopsy

Owners of Warmbloods with debilitating--or sometimes just plain baffling--muscle disorders can get useful and reliable answers about their horses' conditions through a relatively simple muscle biopsy. So say University of Minnesota researchers, who in a recent study also reported that the most common muscle disorders identified in these types of breeds are polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (also known as tying-up).

"Until now, there was only limited information regarding the type of myopathies (muscle disorders) that occur in Warmbloods, the clinical signs associated with myopathies, or how to manage affected horses," said Stephanie Valberg, DVM, PhD, Dipl. ACVIM, professor of large animal medicine and director of the University of Minnesota's Equine Center.

The researchers examined 2,234 muscle biopsies submitted to the University of Minnesota's Neuromuscular Diagnostic Laboratory between January 1996 and September 2006. Among these samples they identified 132 Warmblood or Warmblood-cross horses. Treating veterinarians submitted the biopsies to verify whether the horses' muscle stiffness, soreness, or atrophy could be due to a muscle disease.

An overwhelming 72 (54.5%) of Warmblood horses with a potential muscle disorder were diagnosed with PSSM (see article #11654 for more information). Other horses had recurrent exertional rhabdomyolysis (7), atrophy (7), and other nonspecific myopathies (14), while 32 horses had normal biopsies.

"The most common reasons that the horses had a muscle biopsy performed were due to gait abnormalities, owner's report of 'tying-up,' muscle tremors, or muscle degeneration (atrophy)," reported study author Luanne Hunt, DVM, an internal medicine resident at the University.

Scientists found the best management strategy for Warmbloods affected with these myopathies utilized regular daily exercise a low-starch, fat-supplemented diet

Research on the genetic basis of different forms of PSSM in Warmblood horses is ongoing. Also, University of Minnesota scientists are investigating the cause of another, unrelated muscle disorder, "shivers," in Warmbloods and Draft horses.

The study, "An epidemiological study of myopathies in Warmblood horses," was published in the Equine Veterinary Journal in March 2008.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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