PSVII-30 Impacts of starch and fat concentrations on equine insulin sensitivity

Abstract This study assessed how substituting starch energy for fat energy affects equine insulin sensitivity. A randomized, complete block design with 5 groups of 4 horses was used to evaluate responses to isoenergetic diets containing 7.1, 9.2, 11.5, 12.8 or 14.3% starch (dry matter basis, targeting 1.0–2.2 g starch/kg body weight). Horses were fed twice daily for 21 days, housed in individual box stalls, used in regular riding lessons, and blocked by plane of nutrition (PON), targeting +1 or -1 body condition score in 30 d. On d1 and d21, a hyperglycemic clamp was performed; horses received a jugular glucose infusion to double basal blood glucose concentrations ([Glu]) in 2 h. Samples for blood glucose and insulin determination were collected every 5 m until [Glu] was held at double basal for 30 minutes. Insulin sensitivity index (ISI) and quantitative insulin sensitivity check index (QUICI) were analysed using a general linear model with fixed effects for starch percent, PON, their interaction, and a covariate for number of workouts (WN). There was no effect (P > 0.10) of starch percent, PON, their interaction, or WN on initial or final ISI. Change in ISI scores was significantly affected by PON (P = 0.009) with a tendency for diet and PON interaction (P = 0.091). Initial QUICI was significantly affected by WN (P = 0.030), but no other relationships (P > 0.10) were observed for initial or final QUICI. Change in QUICI was affected by WN (P = 0.042) with a tendency for a PON effect (P = 0.082). The QUICI and ISI scores were significantly related (P < 0.001; R2=0.66), and their relationship did not interact with WN (0.751), experimental period (0.348), diet (P = 0.689) or PON (P = 0.200).