Diurnal variation in plasma metabolite and hormone concentrations and response to metabolic challenges in high breeding index and low breeding index Friesian heifers fed at two allowances

Abstract

Abstract Diurnal variation in blood metabolite and hormone concentrations and their responses to acute intravenous injections of glucose, insulin, glucagon, and adrenaline were examined in twelve 6-8-month-old Friesian heifers born to either high breeding index (HBI) or low breeding index (LBI) parents. Heifers were fed once daily at below (75%) and above ( 125%) their maintenance energy requirement (MER) in a single reversal trial to test the effects of selection line and its interaction with energy balance. The concentration of all the metabolites and hormones measured varied over the day and, when compared with heifers fed 125% MER, those fed 75% MER exhibited: increased plasma creatinine concentrations; a smaller increment in plasma urea concentration after feeding; greater plasma non-esterified fatty acid (NEFA) concentrations in the post-prandial period; and lower insulin concentrations during the 24-h sampling period. Basal concentrations of insulin, creatinine, growth hormone, and NEFA were not in...