Glucose and insulin dynamics in neonatal foals: influence of maternal diet

Abstract

s / Journal of Equine Veterinary Science 31 (2011) 230-356 277 Nutrition: Oral Presentations II Glucose and insulin dynamics in neonatal foals: influence of maternal diet T.N. Dobbs , C.E. Foote , A.J. Cawdell-Smith , S.T. Anderson , R.C. Boston , and W.L. Bryden 1 1 The University of Queensland, Gatton, QLD, Australia, 2 Equine Consulting Services Pty Ltd, Glenorie, NSW, Australia, 3 University of Pennsylvania, Philadelphia, PA, USA Introduction: Pregnancy is characterized by a progressive decline in insulin sensitivity, an adaptation that parallels growth of the feto-placental unit, ensuring sufficient glucose supply to the fetus [1]. Therefore factors, including nutrition that influence maternal insulin sensitivity will alter glucose availability to the fetus. Dietary energy composition, specifically feeds high in nonstructural carbohydrates, are known to diminish insulin sensitivity, increasing risk for diseases such as obesity and laminitis in the horse [2]. Moreover, changes in glucose and insulin dynamics during gestation may predispose the foal to metabolic disorders associated with insulin resistance later in life. The current study investigates the relationship between the diet fed to the mare during the last trimester of pregnancy and the glucose and insulin dynamics of her subsequent foal. Materials and Methods: Pregnant Standardbred mares were used in the study and offered either a normal/low carbohydrate (16.0 Mcal/day of digestible energy (DE), n 1⁄4 6) or high carbohydrate (25.8 Mcal DE/day, n 1⁄4 6) concentrate diet during the last trimester of pregnancy (200-320 days of gestation) with the remainder of DE requirements available from forage. Diets were balanced for mineral content and satisfied NRC recommendations [3]. Monthly blood samples were collected in themorning (0700 to 0900h) to determine basal insulin and glucose concentrations in conjunctionwith body condition score (BCS) and body weight. The insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT) [4] was applied to mares at 320 days of gestation. Neonatal foal FSIGTs (n 1⁄4 11) were conducted at 14 days of age. Results obtained from the FSIGT were used for minimal model analysis of glucose and insulin dynamics and determined parameters of insulin sensitivity (SI), glucose effectiveness (Sg), acute insulin response to glucose (AIRg) and disposition index (DI) [5]. Plasma insulin concentrations were assayed using RIA (CoatA-Count Insulin, Diagnostics Products Corp., Los Angeles, CA); validated for use with equine plasma [6]. Plasma glucose concentrations were analysed enzymatically (Hexokinase method, Olympus kit on an Olympus AU 400 Analyser, Diagnostics Systems Division, Melville NY). Means ( S.E) were calculated for plasma insulin and glucose concentrations, body weights, BCSs and minimal model parameters derived from FSIGT analysis. Statistical significance was assessed using parametric tests including one-way ANOVA with repeated measures for treatment and time comparisons and unpaired t-test for analysis of individual time points. Results and Discussion: odyweight and BCS increased in pregnant mares in the last trimester, with significantly (P 1 year) to determine long term effects of feeding different calorie sources. Therefore, the objective of this study was to test the hypothesis that young horses would have decreased insulin sensitivity when growing on feed higher in sugar and starch, and that further adaptations in insulin sensitivity due to time may become evident.