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Friday, December 14, 2007

Shivers in Draft Breeds and Warmbloods: No Link to PSSM Found

Double-click on the illustration to enlarge it in a new window. This is a great and simple guide to hind leg action caused by various conditions.

The year-end report from the Morris Animal Foundation reached me today, and I will be passing along a couple of nuggets from MAF-funded research that I think might be of interest to blog readers.

This one, in particular piqued my curiosity. Anyone who works around big horses will soon run into a shiverer and there has long been speculation that, since many also suffer from equine polysaccharide storage myopathy (PPSM), many thought that some link must exist between the two.

A shiverer is a horse with a gait and stance problem characterized by compulsive hyperflexing and trembling of the hind leg. Farriers are often the first to identify a shiverer, which becomes a chronic condition and sometimes causes lameness.

Here's the technical description:
Shivers is a devastating disorder in draft and warmblood horses whereby horses develop muscle tremors and hyperflexion beyond normal limits of the rear limbs during shoeing, after standing still or when backing up. Many affected horses also show concurrent tail tremors. In some horses, Shivers never progresses, while in others it leads to weakness, muscle atrophy and an inability to get up that may require euthanasia.

The investigators examined whether Shivers is caused by another painful muscle disorder, equine polysaccharide storage myopathy (PPSM), or whether PPSM and Shivers are common but separate disorders that can coexist in the same horse.

“Polysaccharide Storage Myopathy and Shivers in Draft and Warmblood Horses” was funded by MAF and conducted at the University of Minnesota, under the direction of Stephanie J. Valberg, DVM, PhD. Research was completed in March 2007

Dr. Valberg's report: "There is a high prevalence of both PSSM and Shivers within the Belgian draft horse population.

"Researchers discovered that 36 percent of Belgians in the study suffered from PSSM and the same disease was found in warmblood horses.

"The most common signs of the disease were unexplained lameness, reluctance to engage the hindquarters and muscle stiffness during exercise.

"The team also identified Shivers in 20 percent of Belgian draft horses. This disease causes horses to have trouble backing up because their hind legs become fixed in an elevated, flexed position.

"Researchers learned that contrary to what was previously thought, Shivers is not caused by PSSM."

There's no mention in the report of how many, if any, horses in the study suffered from both PSSM and shivers.

To learn more: Hoofcare and Lameness published a detailed article on PSSM and how it manifests as hind-end lameness in horses in our issue #75. Our author Beth Valentine DVM PhD of Oregon State University College of Veterinary Medicine is a specialist in PSSM and an early investigator of the disease. She carefully differentiated how draft horses display hind end lameness, explaining the hind leg motion of shivers, stringhalt, patellar problems, and PSSM in an attempt to get more horses treatment for PSSM, which can often be helped with simple dietary changes.

The new MAF-funded research motivated me to dig out the old Hoofcare and Lameness article; it is still an excellent paper and makes me wonder about all the horses that people describe to me as shiverers.

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