GROWTH-RELATED HORMONES IN PLASMA OF BULLS, STEERS AND HEIFERS GIVEN FOOD WITH 2 DIFFERENT ENERGY-LEVELS

Concentrations of growth hormone (GH), insulin-like growth factor (IGF -1), insulin and glucagon were determined in the plasma of growing bul ls, steers and heifers (no. = 138 in total, German Simmental breed). T he animals were offered either a high level or a low level of energy r esulting in relatively high and low average daily gain. Trials were su bdivided into two experimental series and started at approximately 3 m onths of age at an average live weight of 110 kg. The animals were sla ughtered at different body weights from 200 to 510 kg (heifers) or 660 kg (bulls, steers). Blood samples (needle puncture) were collected at biweekly intervals. Frequent samples for time-course analysis of GH w ere taken by catheter from nine animals in total. Concentrations of GH declined during growth in steers and heifers as well as in bulls in b lood samples collected by means of a catheter. IGF-I and insulin conce ntrations increased from the start of the trial onwards up to differen t ages among the groups. Concentrations of glucagon constantly decreas ed from the start of the trial until slaughter. Significant difference s (P < 0.05) in concentrations of GH, IGF-1 and insulin could be obser ved between sexes and levels of nutrition, with the highest GH and IGF -1 levels in bulls followed by steers and heifers. In contrast insulin values were highest in heifers followed by steers and bulls. A high l evel of nutrition increased concentrations of IGF-1 and insulin in all sexes.