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 (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 ± 2.2 years; 621 ± 78.8 kg) were individually fed [~1 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 < .001; ID 22 362 ± 10 298 µIU/mL/min & NID 6145 ± 1922 µIU/mL/min). No effect of diet on AUCi for NID (P = .2), but in ID, the CC (32 000 ± 13 960 µIU/mL/min) AUCi was higher than RB-LP (P = .01; 18 977 ± 6731 µIU/mL/min). ID insulin (T60) was lower for the L-NSC (57.8 ± 18.5 µIU/mL) versus all other diets (P < .02; 160.1 ± 91.5 µIU/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.