GROWTH HORMONE (bST), INSULIN, INSULIN LIKE GROWTH FACTOR I (IGF-I) AND IGF-I BINDING PROTEINS DURING LACTATION IN CATTLE

Publisher Summary This chapter describes the growth hormone (bST), insulin, insulin like growth factor I (IGF-I) and IGF-I binding proteins during lactation in cattle. There is clear evidence for the growth hormone family being essential for galactopoiesis in cattle. In high-yielding dairy cows marked endocrine changes occur that are considered responsible for the shift from an anabolic state during late pregnancy towards a primarily catabolic state in early lactation and again to an anabolic state during mid- and late-lactation. Concentrations of bST increased after parturition for about 8 wk, decreased thereafter and reached a lower plateau 18 wk pp and remained at that level for the rest of the lactation. The increase of bST after parturition was related to an enhanced episodic secretory activity of bST. bST levels were positively correlated to milk yield contrary to concentrations of IGF-I and insulin which were negatively correlated. The IGF-I response to exogenous bST was diminished immediately after parturition and increased continuously thereafter. The 45 kDa binding protein of IGF-I seems to be constant throughout lactation.