Antibiotic Virginiamycin Does Not Reduce Cribbing, Weaving

Finding a "cure" for common stereotypies, such as headshaking, cribbing, and weaving, continues to elude veterinary researchers, since the antibiotic virginiamycin as a dietary supplement has been culled from the pool of possibilities.

Stereotypies, repetitive and apparently functionless behaviors, are common in intensively managed horses. They are problematic because they reduce normal rest and eating behaviors and can cause unnatural wear-and-tear.

"Previous research in this field has hypothesized that oral stereotypies are due to a reduction in gastric or hindgut pH levels. Evidence exists that increasing the pH in these anatomic regions decreases the expression of anxiety-related oral behaviors," explained Paul McGreevy, BVSc, PhD, MACVs, MRCVS, from the faculty of Veterinary Science at the University of Sydney.

According to numerous published reports, virginiamycin has been shown to increase the pH in the hindgut of various species, including the horse.

To test the hypothesis that virginiamycin can alter the expression of sterotypies by increasing hindgut pH levels, McGreevy and colleagues evaluated the effect of virginiamycin (5g/100kg bodyweight) compared to a placebo in 17 Thoroughbred geldings, of which five were cribbers, six were weavers, and six control horses that displayed no stereotypies.

"In this study, virginiamycin had no significant effect on cribbing, weaving, frequency of eating, lying down, urinating, defecation, plasma cortisol levels, heart rate, blood glucose peak response, or digestibility of feed," summarized McGreevy.

Virginiamycin-supplemented cribbers had significantly increased water consumption while the weavers had significantly decreased water consumption. Water intake was unaltered in the control group. Reasons for these observations are unclear.

In conclusion, McGreevy stated, "If virginiamycin alters the pH in the hindgut as previously suggested, then this change in acidity does not appear to affect signs of physiological distress or established stereotypies in adult horses."

The study, "Behavioural and physiological effects of virginiamycin in the diets of horses with stereotypies," was published in October 2008 in the journal Veterinary Record.

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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