Blocking Certain Hormones: Key to Equine Laminitis?

Horses and ponies with insulin dysregulation produce too much insulin in response to dietary carbohydrates and, over time, often leads to laminitis. Though researchers can document these insulin spikes easily enough, they do not know why they occur. Researchers recently looked closely at a specific hormone that might help unlock the insulin-laminitis mystery.

In all horses, this hormone, glucagon-like peptide-1 (GLP-1), is released from the intestinal wall during digestion of certain carbohydrates, and release of GLP-1 helps stimulate pancreatic insulin production. Horses prone to laminitis have shown greater plasma GLP-1 in response to grain meals, but researchers did not know whether GLP-1 was actually responsible for the extreme insulin response. Therefore, they set out to block GLP-1 receptors to determine if the hormone plays an important role in excessive insulin excretion in horses diagnosed with insulin dysregulation when fed a high-glycemic meal.*

Five mature, obese ponies known to have insulin dysregulation were given a feed challenge. They were administered a GLP-1 receptor-blocking peptide, known to block the activation of the receptor in several species and in in vitro studies of equine pancreatic explants (cells or tissues). Ponies were then fed a high-starch meal containing micronized corn, soybean hulls, and alfalfa (lucerne) chaff. Insulin, glucose, and GLP-1 were measured in blood samples.

The results? First, this study confirmed that high levels of GLP-1 in horses with insulin dysregulation contribute to excessive insulin production. Second, blocking the receptor partially reduced insulin production in response to a high-starch diet. It is not known whether the amount of receptor blocker was optimal, meaning it might be possible to achieve an even greater blocking effect, though this would require more study with varying doses. As it stands, GLP-1 receptors are a “potential therapeutic target for preventing laminitis,” according to the researchers.

Every scientific study takes us one step closer to understanding the role of insulin in laminitis. “Until a cure is found, management remains a key strategy for horses with insulin dysregulation or those predisposed to it,” said Catherine Whitehouse, M.S., a nutritionist at Kentucky Equine Research.

Key management strategies include:

• Keeping your horse in moderate body condition, which means being able to easily feel its ribs without necessarily seeing them. “Horses are individuals, so some leeway here is necessary, but horses should not be roly-poly, as this may make them more susceptible to metabolic issues,” said Whitehouse. Be especially mindful with horses known to be easy keepers, such as Morgans, Arabians, and many stock-type breeds. Refer to the Henneke body condition scale if you’re not comfortable recognizing moderate body weight. Using that scale, horses should be a 5 (moderate).

• Feeding your horse the diet he requires. Easy keepers with a casual lifestyle might do well on good-quality forage and a vitamin and mineral supplement. Horses should be fed energy-dense concentrates, like commercial feeds, to help fuel growth, performance, or lactation and to provide key nutrients for physiological processes not applicable to idle easy keepers, explained Whitehouse.

• Selecting a vitamin and mineral supplement, such as Micro-Max (Gold Pellet, Nutrequin, or Perform in Australia) for horses not fed a commercial feed. A well-formulated vitamin and mineral supplement will round out the nutritional needs of horses on all-forage diets.

• Exercising your horse as often as five or six days a week, if soundness allows. Researchers believe that at least 30 minutes of exercise with elevated heart rate can help keep metabolic problems from appearing.

• Use of omega-3 fatty acids, such as the marine-derived sources found in EO-3, can help with insulin sensitivity, and EquiShure, a hindgut buffer, can support health of the cecum and colon.

• Enlisting the help of a knowledgeable veterinarian and an equine nutritionist. These professionals can help you make key decisions about health and management. “As a professional nutritionist, it’s my goal to help people make the best nutritional decisions for their horses,” Whitehouse said.

Learn more about managing metabolic diseases in Nutritional Management of Metabolic Diseases, a booklet developed by Kentucky Equine Research.

Are you looking for more specific nutrition advice? Contact one of the nutrition advisors at Kentucky Equine Research today!

*Fitzgerald, D.M., M.A. De Laat, P.A. Harris, and S.R. Bailey. 2018. Effect on plasma insulin of a peptide inhibitor of the incretin hormone, GLP-1, in ponies fed a meal containing micronized maize. In: Proc. Australasian Equine Science Symposium 7:19.