EFFECTS OF SEX AND GROWTH ON PLASMA-CONCENTRATIONS OF GROWTH-HORMONE, INSULIN-LIKE GROWTH FACTOR-I AND INSULIN IN FATTENING SIMMENTAL CATTLE

Concentrations of growth hormone (GH), insulin-like growth factor (IGF-I) and insulin were determined in plasma of growing bulls, steers and heifers (German Simmental breed). Trial was subdivided into three experimental phases and started with approximately three month of age at a body weight (BW) averaging 110 kg. Final slaughter weight was 510 kg (heifers) and 660 kg (bulls, steers). Blood samples (needle puncture) were collected in biweekly intervals. Significant differences (p < 0.05) between sexes could be observed in GH, IGF-I and insulin concentrations. Bulls showed highest GH and IGF-I concentrations, followed by steers and heifers. Heifers had highest insulin concentrations, followed by steers and bulls. Concentrations of GH declined during growth in steers and heifers, whereas in bulls, concentrations of GH was possibly influenced by stress and therefore only in tendency affected by growth. IGF-I and insulin concentrations increased with progressive weight. Levels and alterations of these hormones are discussed with regard to growth an sex. Furthermore, physiological effects of hormones and their concentrations in relation to carcass composition suggest that IGF-I (somatotropin axis respectively) is associated to protein accretion and lean percentage in carcass, whereas fat deposition and degree of fatness in carcass is more related to insulin.