A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome

Equine metabolic syndrome (EMS) is characterized by an abnormal insulin response to a glycemic challenge but despite the known insulinotropic effects of certain amino acids, there is a paucity of data evaluating the impact of dietary protein on insulin dynamics in these horses. The objective was therefore to assess insulin and amino acid responses following intake of a high protein meal in healthy horses and those with EMS. Six mature horses diagnosed with EMS and six age-matched control horses without EMS were used. Horses were fed 2 g/kg body mass (BM) of a high protein pellet (31% crude protein) at time 0 and 30 min, for a total of 4 g/kg BM, following an overnight fast. Blood samples collected during a 4 h period were analysed for plasma glucose, insulin, amino acids and urea concentrations. Glucose concentrations were not different between groups (P = 0.2). Horses with EMS had a 9-fold greater insulinemic response to the consumption of a high protein meal compared with controls (P = 0.046). Post-prandial levels of histidine, citrulline, tyrosine, valine, methionine, isoleucine, leucine and ornithine were higher in horses with EMS (P < 0.05). Baseline urea nitrogen concentrations were not significantly different between groups (P = 0.1). Knowing that certain amino acids are insulin secretagogues, these results illustrate that consumption of a high protein meal caused a hyperinsulinemic response and affected amino acid dynamics in horses with EMS. These findings suggest that dietary protein content should be taken into consideration in the management of horses with insulin dysregulation.