EFFECTS OF SEASON, PROTEIN AND NUTRITIONAL STATE ON GLUCOSE-TOLERANCEDURING AN ANNUAL CYCLE OF GROWTH IN YOUNG RED DEER STAGS

Two hypotheses were tested in gonad-intact, young (aged 6-18 months), growing red deer stags during an annual growth cycle. First, that gluc ose clearance rate is faster during summer than during winter. Secondl y, that increased dietary protein availability will enhance winter gro wth. Stags were randomly assigned into one of two groups: group 1 (n=5 ) had 16% while group 2 (n=6) had 48% of dietary protein naturally pro tected against fermentative degradation in the rumen. Total crude prot ein and energy remained similar for each diet (12 and 14% respectively for protein and 11 MJ metabolisable energy/kg dry matter). Stags were kept indoors in individual pens for 12 months and given monthly intra venous glucose tolerance tests (IVGTT), at a dose of 200 mg/kg, in the fed and fasted (48 h) states to determine both growth and steady-stat e tissue requirements. Protein level had no effect on food intake, wei ght gain, insulin kinetics, or glucose clearance rate. In the fed stat e, insulin peak (highest level after IVGTT) increased (P<O.01) from Oc tober (139 pmol/l) to December (247 pmol/l) (S.E.D. = 42) and remained elevated during the summer, before declining (P<O.01) from February ( 223 pmol/l) to April (130 pmol/l) (S.E.D. = 25). Glucose clearance rat e was faster (P<0.05) in December (1.69 litres/min) than June (0.61 li tres/min) in the fed state (S.E.D.= 0.30), and decreased (p<0.05) from February (1.75 litres/min) to April (0.92 litres/min) (S.E.D. = 0.39) . During fasting, the pattern of glucose clearance was similar to that observed in the fed state, but the amplitude was lower, while the pat tern for insulin peak was similar to that of the fed state. We conclud ed first, that additional protected protein does not benefit growth du ring winter. Secondly, we concluded from the fasted, steady-state data that stags are insulin resistant during summer. Thirdly, despite insu lin resistance, data on the fed state demonstrated that stags have hig her tissue energy requirements during summer growth.