Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non-insulin dysregulated controls

Background: Controlling postprandial hyperinsulinaemia is important in insulin dysregulated (ID) horses to reduce the risk of laminitis. Objectives: To evaluate postprandial insulin responses of ID versus non-insulin dysregulated (MD) horses to feedstuffs varying in nonstructural carbohydrate (NSC) and crude protein (CP). Study design: Randomised crossover. Methods: Eighteen adult mixed-breed horses (13.3 +/- 2.2 years; 621 +/- 78.8 kg) were individually fed [similar to 1 g/kg body weight (BW)] specific feedstuffs within two crossover studies. Eight ID and eight MD were used in Study A, and 11 ID and 5 NID in Study B. In Study A, all horses were randomly fed once: cracked corn (CC: similar to 74% NSC & similar to 9% CP), ration balancer with low protein (RB-LP: similar to 15% NSC & similar to 17% CP), ration balancer with high protein (RB-HP: similar to 14% NSC and similar to 37% CP) and 50:50 mixture of RB-LP:RB-HP (MIX-P). In Study B, horses were randomly fed once: CC, RB-HP, steam-flaked corn (SF: similar to 73% NSC & similar to 10% CP), oat groats (OG: similar to 64% NSC & similar to 14% CP) and a low NSC pellet (L-NSC: similar to 6% NSC & similar to 12% CP). Blood was collected for insulin determination [radioimmunoassay (RIA)] before and 30, 60, 75, 90, 105, 120, 150, 180, 210 and 240-minute post-feeding in Study A and at 60-minute in Study B. Data were analysed via analysis of variance (ANOVA) for repeated measures after any required transformations. Results: ID horses had significantly greater insulin responses (AUCi) than NID for all diets in both studies (P < .001; ID 22 362 +/- 10 298 plU/mUmin & NID 6145 +/- 1922 plU/mL/min). No effect of diet on AUCi for NID (P = .2), but in ID, the CC (32 000 +/- 13 960 ji1U/mUmin) AUCi was higher than RB-LP (P = .01; 18 977 -+/-- 6731 mu lU/mL/min). ID insulin (T60) was lower for the L-NSC (57.8 +/- 18.5 mu lU/mL) versus all other diets (P < .02; 160.1 +/- 91.5 mu lU/mL). Main limitations: Small numbers of horses; no ponies. Conclusions: NSC appears to be the main driver of the postprandial insulin response. ID horses respond disproportionately to feeding even small amounts of low/moderate NSC feedstuffs. Data on possible dietary thresholds for postprandial insulin responses cannot be extrapolated from NID horses.