Understanding the Effects of Varying Nutrient Content in Forage on Postprandial Insulin Responses in Equine Metabolic Syndrome horses

Insulin dysregulation (ID) is characterized by increased insulin responses to oral sugars, hyperinsulinemia or tissue insulin resistance. It is most often associated with equine metabolic syndrome (EMS), which predisposes horses to laminitis. Laminitis is a devastating inflammatory condition that causes severe pain and often leads to euthanasia. Similar to humans, vast amounts of nutrients are available to horse owners, which often leads to equine obesity and the development of insulin dysregulation. Furthermore, and of great importance to the industry, it remains to be determined how to nutritionally manage EMS horses in order to control the postprandial response in ID horses. While it is recommended to maintain ID horses on a forage only diet, no research has been conducted to determine the effects of forage nutrient content on insulin responses in EMS horses. More specifically, it remains to be determined what level of non-structural carbohydrates and protein in forage will cause an exaggerated metabolic response in ID horses compared to metabolically normal horses. Based on our preliminary data there is a significant difference in ID horses’ responses to varying NSC and protein content compared to healthy, control animals; however, we do not know if they would produce the same response when fed a forage vs. concentrate. Thus, the objectives of the proposed study are the following: 1) to determine what levels of nutrients (non-structural carbohydrates (NSC) and crude protein) from forage (hay pellets) affect insulin responses in horses with insulin dysregulation associated with EMS compared to metabolically, healthy adult horses and 2) to determine the mechanism that may contribute to differences in insulin response to varying nutrients by measuring insulin, glucose, incretins, and c-peptide. Sixteen horses will be screened for the presence of ID and pituitary pars intermedia dysfunction (PPID), via a oral sugar test and basal ACTH measurement, respectively. Two groups will be used, healthy controls (n=8) & ID horses (n=8). Horses will be weighed, body condition scored (BCS) and cresty neck scored (CNS). Horses will be randomly selected to eat one of the two types of hay pellets, alfalfa pellets & timothy hay pellets or dehulled oats. An even amount of horses will be represented in each group during the acclimation and testing periods. The proposed study is a crossover design, where all horses will consume timothy hay pellets, alfalfa hay pellets, and de-hulled oats at random during the 3 feeding periods. Feeding periods are composed of acclimation days and the testing day, where there will be 4 acclimation days and 1 testing day for each feeding period. During acclimation, horses will receive 30% of their total ration. On test day, horses will receive diets based on g of NSC/kg BW. In the morning hours, horses will be brought into individual pens and be fasted for 3-hours. After the fast has finished, horses will have a basal blood sample (T0) taken and then the diet will be offered. After the consumption of the treatment diet, blood will be drawn at 60, 90, and 120 minutes. Blood will be analyzed for insulin, glucose, c-peptide and incretins. Hay pellets and de-hulled oats will be analyzed by Equi-Analytical Forage Laboratory throughout acclimation and on test day. Statistics will be analyzed by SAS. ID and control animals will be compared via a repeated measure two-way ANOVA with metabolic status (ID & control) and diet as levels for all metabolites. Delta insulins will be calculated for each horse to see the change from baseline to 120 minutes. We expect that ID horses will have elevated levels of insulin, glucose, c-peptide, and incretins to both the forage type with higher NSC. Insulin area under the curve will be significantly different from horses, as well as the other metabolites revealing clues to the mechanism of the postprandial response. This will allow for us to begin to provide science based recommendations to the industry on what types of forage to feed to metabolically challenged horses in order to control the postprandial responses in ID horses. While there are many potential factors that could affect insulin, none of them are as important as nutrition. Given laminitis is a severely painful and potentially crippling disease that is oftentimes fatal there is a critical need to establish how to nutritionally manage these horses in order to control insulin dysregulation and the development of laminitis.