Insulinemic responses to long-stem forage hay in horses with insulin dysregulation (ID)

Abstract

Maintaining healthy postprandial responses in insulin dysregulation (ID) horses is key to preventing hyperinsulinemia-associated laminitis. This study investigated meal feeding preserved forage (hay) with different nonstructural carbohydrate (NSC) content on the insulin responses in ID versus non-insulin dysregulated (NID) horses basally fed low-NSC hay plus a balancer. Ten horses were categorized as ID (n = 5; 593 ± 95.3kgs) or NID (n = 5; 607.6 ± 68.4 kg). The randomized 5-wk crossover study comprised 2 treatments per week. Six diets were fed once per horse: a positive control (oat groats [OG]; 546 g NSC/kg as-fed); a negative control (low-NSC pellet [LNSC]; 75 g NSC/kg as-fed); and 4 forages: orchardgrass hay (OH; 64 g NSC/kg as-fed); alfalfa hay (AH; 67 g NSC/kg as-fed); timothy hay 1 (TH1; 90 g NSC/kg as-fed); and timothy hay 2 (TH2; 163 g/kg as-fed). Control and forage diets were fed at 1.0 g and 2.0 g/kg BW per meal, respectively, after an overnight fast on a drylot with ad libitum water. This resulted in meal NSC intakes (g/kg BW) of 0.07 for LNSC, 0.13 for OH, 0.135 for AH, 0.18 for TH1, 0.33 for TH2, and for 0.55 OG. Blood samples were collected before feeding and after consumption of the meal at 0 (meal completion), 60, 90, 120, 180, and 240 min. Blood samples were analyzed for insulin by automated immunoassay analyzer (Tosoh). A 2-way ANOVA was performed using GraphPad Prism. Data were log-transformed to achieve normality. Statistical significance was considered at P < 0.05, and data are presented as the mean ± SEM. All meals were consumed in 10 ± 1 min for controls and 45 ± 2 min for forages. Peak and delta insulin for ID horses were greater (P < 0.05) for all dietary treatments compared with NID. The ID and NID horses’ peak insulin were higher for OG (ID: 725.3 ± 169.6 μIU/mL; NID: 31.2 ± 7.9 μIU/mL) compared with all other feedstuffs (P < 0.01). In addition, TH1 and TH2 peak insulin for ID horses was higher than LNSC (109.0 ± 18.2; 134.0 ± 34.7; 45.9 ± 5.0 μIU/mL respectively, P < 0.01). Delta insulin was also higher for OG than all other feedstuffs for both ID (693.2 ± 170.6 μIU/mL) and NID (25.5 ± 7.1 μIU/mL; P < 0.01). For the NID delta insulin was also higher for TH2 (7.1 ± 2.3 μIU/mL) than OH (3.6 ± 3.0 μIU/mL; P < 0.01). For the ID horses the delta insulin for the LNSC (14.8 ± 3.6 μIU/mL) was significantly lower than AH (45.0 ± 6.9 μIU/mL), TH1 (80.5 ± 17.0 μIU/mL), and TH2 (99.7 ± 29.9 μIU/mL), but not OH (38.3 ± 8.1 μIU/mL). Insulin responses to hay were individually variable. Despite AH and TH1 having NSCs of ≤9% on an as-fed basis (∼10% DM) there was an augmented insulin response compared with the LNSC. Results suggest that feeding a forage >0.13 g NSC/kg BW per meal may produce an augmented insulin response in ID horses. Further work is needed to investigate feeding larger amounts of long-stem forages on insulin responses.