Reversing Insulin Dysregulation in Horses, Ponies

Obese horses and ponies have a higher chance of developing health issues such as insulin dysregulation, a prominent characteristic of metabolic syndrome. Whether or not insulin dysregulation can be reversed once it develops remains unclear, but one recently published study suggests that it can.^*

The reversal of insulin dysregulation was demonstrated using Shetland ponies, which are known for their propensity to gain weight and develop insulin dysregulation. After feeding the ponies twice their net energy requirements, body weight increased by 27% over a 24-week period. Once weight gain was achieved and all ponies had a body condition score of at least 7 out of 9, an increase in insulin response was noted. This means that more insulin was required to control circulating blood sugar levels after consuming concentrates rich in nonstructural carbohydrates and fat.

When the diets of the ponies were switched from the high-energy diet to a roughage-only diet for the next 17 weeks, the ponies did not lose significant amounts of weight. Despite no weight loss, changing the diet from one rich in nonstructural carbohydrates and fat to one of only forage reversed the insulin dysregulation, which was not expected.

Then, ponies were again fed a diet rich in sugar, starch and fat. Insulin dysregulation and hyperinsulinemia returned promptly, and were more exaggerated than after the first round of excessive feeding. Further, all ponies exhibited a shortened stride and stiff movement indicative of subclinical laminitic changes at this point in the study.

“This study makes it clear that excessive feeding with high-starch and high-fat diets for a long duration can have detrimental effects and increase the chances of endocrine-associated laminitis,” advised Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Avoiding weight gain and obesity, particularly in breeds predisposed to equine metabolic syndrome, will play a key role in avoiding insulin dysregulation. Here are some ways to help maintain moderate body condition:

• Familiarize yourself with how to accurately assess body condition score;
• Have hay analyzed to ensure you are not overfeeding nonstructural carbohydrates. A forage with 10-12% nonstructural carbohydrates will suffice for most horses, particularly those at-risk for obesity and metabolic syndrome;
• Limit or avoid pasture intake (use grazing muzzles or drylots), and offer minimal treats, sweet feeds, and concentrates; and
• Implement an exercise program.

For horses requiring a supplement to balance a forage-based diet, Crandell recommends offering a low-intake concentrated source of high-quality vitamins and minerals.

^*d’ Fonseca, N.M.M., C.M.E. Gibson, D.A. van Doorn, M. de Ruijter-Villani, T.A.E. Stout, and E. Roelfsema. 2020. Effect of long-term overfeeding of a high-energy diet on glucose tolerance in Shetland pony mares. Journal of Veterinary Internal Medicine 34:1339-1349.