Insulin responses to various feedstuffs differ in insulin dysregulated horses

In this study we find some new information on how sensitive insulin dysregulated horses (PPID and metabolic syndrome horses). Postprandial insulin responses to various feedstuffs in insulin dysregulated (ID) horses are compared to non-insulin dysregulated (NID) controls. Not surprisingly the results showed that the insulin response in horses with ID are greater to the presence of non-structural carbohydrates (NSC). What is surprising is the degree of increase in the insulin response and how little NSC it takes to create this exaggerated response. For more on feeding IR horses see the article above.
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Equine Vet J. 2021 May 30.
Authors
Erica L Macon 1 , Patricia Harris 2 , Simon Bailey 3 , Virginia D Barker 1 , Amanda Adams 4
Affiliations

1 108 M. H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY, 40546, USA.
2 Equine Studies Group, WALTHAM Petcare Science Institute, Freeby Lane, Waltham-on-the-Wold, Leicestershire, LE14 4RT, UK.
3 Melbourne Veterinary School, Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Parkville, Victoria, 3010, Australia.
4 MARS Equestrian Research Fellow, Department of Veterinary Science, M. H. Gluck Equine Research Center, University of Kentucky, Lexington, KY, 40546, USA.

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 vs. non-insulin dysregulated (NID) horses to feedstuffs varying in non-structural carbohydrate (NSC) and crude protein (CP).

Study design: Randomised crossover.

Methods: 18 adult mixed-breed horses (13.3 ± 2.2 years; 621 ± 78.8 kg) were individually fed (~1g/kg BW) specific feedstuffs within two crossover studies. 8ID & 8NID were used in Study A and 11ID & 5 NID in Study B. 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). 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 (RIA) before and 30, 60, 75, 90, 105, 120, 150, 180, 210, and 240 minutes post-feeding in study A and at 60-minutes in study B. Data were analysed via ANOVA for repeat measures post any required transformations.

Results: ID horses had significantly greater insulin responses (AUCi) than NID for all diets in both studies (p<0.001; ID 22,362 ± 10,298 µIU/mL·min & NID 6,145 ± 1,922 µIU/mL·min). No effect of diet on AUCi for NID (p=0.2) but in ID the CC (32,000 ± 13,960 µIU/mL·min) AUCi was higher than RB-LP (p=0.01; 18,977 ± 6,731 µIU/mL·min). ID insulin (T60) was lower for the L-NSC (57.8 ± 18.5 µIU/mL) vs. all other diets (p<0.02; 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.

Keywords: horse.