Older Horses Doing Poorly Could Have Diabetes

Historically a rare disease, type 2 diabetes mellitus should be considered an important differential diagnosis in mature or elderly horses and ponies with weight loss and excessive drinking and urinating, advised a team of veterinarians led by Andy Durham, BSc, BVSc, CertEP, DEIM, Dipl. ECEIM, MRCVS. The team consisted of vets from England, Ireland, and the U.S.

Diabetes mellitus (DM) is a chronic elevation of blood glucose (sugar) levels. The hormone insulin, produced by the pancreas, usually maintains blood-sugar levels within very tight limits. Diabetes results due to defects in insulin secretion, action, or both.

According to Durham et al., type 2 DM (T2DM) results from a gradual onset of insulin resistance and pancreatic β cell failure (i.e., inability to produce insulin) that is only rarely diagnosed in equine practice.

Considering the recent increased awareness of insulin resistance and equine metabolic syndrome in horses, the veterinarians hypothesized that T2DM might be more common than currently speculated.

Using a specific and quantitative method to assess insulin sensitivity and pancreatic β cell response called a MINOMOD analysis of the intravenous glucose tolerance test (FSIGTT) in three horses, the veterinarians diagnosed all three with end-stage T2DM. The horses were then treated with a multimodal treatment approach that included dietary modification, metformin, glibenclamide, and/or pergolide.

Treatment successfully restored normal blood glucose levels in all three cases. Durham and co-workers concluded that "T2DM in horses may be more common than generally considered. In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function."

While equine vets are encouraged to consider T2DM in older horses and ponies with clinical signs consistent with DM (e.g., weight loss, excessive drinking, and urination), practitioners need to use caution when it comes to treatment. Since two of the three horses suffered possible adverse side effects, the authors did note that "more investigation into the pharmacologic management of these cases is needed."

This caution was echoed in a commentary on the study by Nicola Menzies-Gow, MA, VetMB, Dipl. ECEIM, Cert EM (internal medicine), PhD, MRCVS from the Royal Veterinary College, who stated: "(A)ntihpyerglycaemic drugs should be used with caution until further pharmacokinetics and bioavailability studies are undertaken in the horse."

Overall, Menzies-Gow did agree that T2DM does appear to be more common than previously thought and is possibly associated with equine Cushing's syndrome (pituitary pars intermedia dysfunction, PPID).

The study, "Type 2 diabetes mellitus with pancreatic β cell dysfunction in 3 horses confirmed with minimal model analysis," and the commentary, "Diabetes in the horse: A condition of increasing clinical awareness for differential diagnosis and interpretation of tests," were both published in the December 2009 edition of the Equine Veterinary Journal. The abstract for the study is available on PubMed.

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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