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

Abstract

Controlling postprandial hyperinsulinaemia is important in insulin dysregulated (ID) horses to reduce the risk of laminitis. To evaluate postprandial insulin responses of ID versus non-insulin dysregulated (NID) horses to feedstuffs varying in nonstructural carbohydrate (NSC) and crude protein (CP). Randomised crossover. Eighteen adult mixed-breed horses (13.3±2.2years; 621±78.8kg) were individually fed [~1g/kg body weight (BW)] specific feedstuffs within two crossover studies. Eight ID and eight NID 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: ~74% NSC & ~9% CP), ration balancer with low protein (RB-LP: ~15% NSC & ~17% CP), ration balancer with high protein (RB-HP: ~14% NSC and ~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: ~73% NSC & ~10% CP), oat groats (OG: ~64% NSC & ~14% CP) and a low NSC pellet (L-NSC: ~6% NSC & ~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. ID horses had significantly greater insulin responses (AUCi) than NID for all diets in both studies (P<.001; ID 22362±10298µIU/mL/min & NID 6145±1922µIU/mL/min). No effect of diet on AUCi for NID (P=.2), but in ID, the CC (32000±13960µIU/mL/min) AUCi was higher than RB-LP (P=.01; 18977±6731µIU/mL/min). ID insulin (T60) was lower for the L-NSC (57.8±18.5µIU/mL) versus all other diets (P<.02; 160.1±91.5µIU/mL). Small numbers of horses; no ponies. 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.