Q: My 9-year-old Missouri Fox Trotter gelding has steadily put on weight throughout his life, even though he is exercised two to three times a week on the trail at working gaits. He is free-fed Bermuda grass hay (not coastal) and no supplements, but he has developed a crest and fatty deposits on his body. My veterinarian tested his thyroid levels, and they were on the high side of normal. She has had him on thyroid powder for the last eight months and his weight has held steady. The tests for insulin resistance and Cushing's disease are expensive--can I treat him and see if that helps? I am unable to cut back on his feed because he starts showing signs of ulcers. Do you have any suggestions?      Kris, via e-mail

A: First, I highly recommend that you assess your horse for insulin resistance (IR). The screening test for IR only costs about $30 and consists of simply drawing a blood sample in the morning (both glucose and insulin levels should be measured). This will allow you to assess the IR situation and monitor your horse's progress.

Obese horses should be taken off pasture, except for very short (30-minute) turnout periods two or three times a day for exercise, and a grazing muzzle should be used at these times. Obese horses should also be ridden as often as possible, which you have already been doing. From a dietary standpoint, you must consider more stringent measures to lower his risk for laminitis. Grain, pellets, and treats (except for a protein, vitamin, and mineral supplement) must be eliminated, and you should try to purchase hay that has a lower sugar and starch content. Hay can be analyzed for approximately $35 and the Equi-Analytical Laboratory is recommended.

You must also restrict the amount of hay fed until the horse loses weight. Start with 1.5% of current body weight (20 pounds for your 1,300-pound horse) and then lower the amount fed to 1.5% of ideal body weight (17 pounds for an ideal weight of 1,100 pounds) over a four-week period.

Your concerns about behavior and gastric ulcers are understandable, so you must try to find innovative ways of managing this. Consider placing another horse in the same paddock or varying the housing location. Our research has shown that levothyroxine sodium (Thyro-L, Lloyd, Inc.) can be given at a higher dosage for three to six months to accelerate weight loss in situations such as this one. This is likely to be a higher dosage than the one you are currently using, so discuss this strategy with your veterinarian.

About the Author

Nicholas Frank, DVM, PhD, Dipl. ACVIM

Nicholas Frank, DVM, PhD, Dipl. ACVIM, is a professor of large animal internal medicine and chair of the department of clinical sciences at the Cummings School of Veterinary Medicine, Tufts University, Massachusetts. His research interests include laminitis, metabolic disorders, PPID/equine Cushing’s, and many other internal-medicine related areas.

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