Plasma concentrations of FSH and LH in entire and castrated prepubertal bull calves treated with Gn-RH

Abstract

In bulls there was no increase in plasma follicle stimulating hormone [FSH] and only a small increase in luteinizing hormone [LH] over the 1st 14 wk of age. In steers (castrated) plasma LH and FSH were unchanged for the 1st 3 wk but increased significantly at 7 and 14 wk. After 100 .mu.g gonadotropin releasing hormone [Gn-RH], LH release in bulls was minimal until 7 and 14 wk and there was no comparable rise for FSH. LH and FSH responded to Gn-RH throughout the trial in the steers. The neonatal calf testes selectively inhibited the release of FSH from the pituitary even when challenged with Gn-RH.