Thyroid Supplement Effective Addition to Equine Weight Loss Program

Researchers from Tennessee recently reported that daily administration of a high dose of levothyroxine sodium--a synthetic thyroid hormone supplement--for 48 weeks resulted in significant weight loss and an improvement in horses' insulin sensitivity.

Insulin resistance, the failureof body tissues to respond appropriately to normal levels of insulin (improper uptake of glucose), is associated with obesity and pasture-associated laminitis. Obese ponies and horses, which are at an increased risk for pasture-associated laminitis, benefit from exercise programs and dietary changes as part of a weight management program. According to Nicholas Frank, DVM, PhD, associate professor in the Department of Large Animal Clinical Sciences at the University of Tennessee's College of Veterinary Medicine, "Dietary changes, exercise, and eliminating or limiting access to pasture are the most important recommendations for obese horses with insulin resistance."

In horses suffering from repeated episodes of laminitis that prevent them from being exercised, levothyroxine sodium could be prescribed by veterinarians over a period of three to six months to enhance weight loss.

In this study, which was funded by Lloyd Inc., the manufacturers of the levothyroxine sodium supplement Thyro-L, six healthy mares received a daily dose of 48 mg of levothyroxine for 48 weeks. The horses lost an average of 25 kg during the study, an amount described as significant.

An increase in the horses' sensitivity to insulin was also noted. Insulin sensitivity increased by 1.8, 2.4 and 1.9 times the pre-treatment levels at weeks 16, 32, and 48, respectively. Further research is required to confirm this correlation, however, as dietary and environmental factors might have influenced results. The impact of this influence could not be accounted for because a control group was not included.

"Levothyroxine sodium induced weight loss and improved insulin sensitivity in healthy nonobese mares," summarized Frank. "We are now studying its effects in horses with equine metabolic syndrome."

The study, "Effects of long-term oral administration of levothyroxine sodium on glucose dynamics in healthy adult horses," was published in the January 2008 edition of the American Journal of Veterinary Research.

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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