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

Abstract

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 (NID) horses to feedstuffs varying in nonstructural carbohydrate (NSC) and crude protein (CP). STUDY DESIGN: Randomised crossover. METHODS: Eighteen adult mixed-breed horses (13.3&#xa0;&#xb1;&#xa0;2.2&#xa0;years; 621&#xa0;&#xb1;&#xa0;78.8&#xa0;kg) were individually fed [~1&#xa0;g/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. RESULTS: ID horses had significantly greater insulin responses (AUCi) than NID for all diets in both studies (P&#xa0;<&#xa0;.001; ID 22&#xa0;362&#xa0;&#xb1;&#xa0;10&#xa0;298&#xa0;&#xb5;IU/mL/min & NID 6145&#xa0;&#xb1;&#xa0;1922&#xa0;&#xb5;IU/mL/min). No effect of diet on AUCi for NID (P&#xa0;=&#xa0;.2), but in ID, the CC (32&#xa0;000&#xa0;&#xb1;&#xa0;13&#xa0;960&#xa0;&#xb5;IU/mL/min) AUCi was higher than RB-LP (P&#xa0;=&#xa0;.01; 18&#xa0;977&#xa0;&#xb1;&#xa0;6731&#xa0;&#xb5;IU/mL/min). ID insulin (T60) was lower for the L-NSC (57.8&#xa0;&#xb1;&#xa0;18.5&#xa0;&#xb5;IU/mL) versus all other diets (P&#xa0;<&#xa0;.02; 160.1&#xa0;&#xb1;&#xa0;91.5&#xa0;&#xb5;IU/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.