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 2g/kg body mass (BM) of a high protein pellet (31% crude protein) at time 0 and 30min, for a total of 4g/kg BM, following an overnight fast. Blood samples collected during a 4h 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.

The effect of dietary fibre on hydration status after dehydration with frusemide.

Three diets were fed to 6 horses in a 3 x 6 Latin rectangle experiment to determine if dietary fibre could improve hydration status in response to dehydration with frusemide. Frusemide was used to simulate dehydration from exercise-induced sweat loss. Diets contained similar dry matter (DM), energy, protein and electrolyte content, but differed in total dietary fibre (TDF) and/or soluble fibre (SDF). The 3 diets were: 1) HIGH-HIGH (high TDF, high SDF); 2) HIGH-LOW (high TDF, low SDF); and 3) LOW-LOW (low TDF, low SDF). In each 10 day period, water intake and faecal moisture content were assessed on Day 7. On Day 10, feed and water were withheld and horses were dehydrated with frusemide (1 mg/kg bwt, i.m.). Plasma volume (PV), plasma total protein (TP), packed cell volume (PCV) and plasma electrolyte concentrations were determined before and after frusemide administration. Water consumption was greater (P < 0.05) when horses received diets high in TDF. Faecal moisture content was greatest (P < 0.01) when horses received the HIGH-HIGH diet. The decline in PV and the rise in plasma TP concentration following frusemide administration were similar for all diets. When horses received the HIGH-HIGH diet, they had a greater (P < 0.05) bodyweight before dehydration and lost more (P < 0.05) bodyweight in response to frusemide. A greater loss of bodyweight in response to frusemide without a proportional loss of PV when horses received the HIGH-HIGH diet suggests that a diet high in SDF may provide the horse with a source of dispensable water in the hind gut during dehydration.

The effect of diet composition and feeding state on the response to exercise in feed-restricted horses.

Eight Thoroughbred horses were used to determine the effects of long-term calorie restriction and diet composition on serum T4 and T3 concentrations and metabolic responses with exercise. Horses were randomly assigned to 2 treatment groups (n = 4): Group 1, horses were fed a calorie-restricted diet designed to have 70% of the calories from the roughage source (RHR); Group 2, horses were fed a calorie-restricted diet designed to have 70% of the calories from the concentrate source (RHC). Horses then completed 2 step-wise exercise tests; one following a 12 h fast and one 2 h after a meal of 2 kg of a grain mix. Glucose concentrations declined (P < 0.01) in fed horses on the RHR diet but did not change in fed horses on the RHC diet. Fasted horses receiving the RHR diet had a more rapid increase in glucose concentration during exercise compared to fasted horses receiving the RHC diet (P < 0.01) as well as the highest glucose concentration at fatigue (P < 0.05). Insulin concentrations were higher (P < 0.05) at fatigue in fed horses on the RHR diet. Fasted horses receiving the RHR diet had higher (P < 0.01) pre-exercise FFA concentrations and a more rapid decline (P < 0.01) in FFA during exercise. Serum T3 concentrations increased (P < 0.01) in response to exercise within all treatments. The differences in thyroid hormone, glucose and FFA responses to exercise suggest that calorie source may be important in the hormonal regulation and energy metabolism of horses consuming calorie deficient diets.