Gonadal regulation of LH secretion in prepubertal bull calves

In the present study we examined the influence of castration and exogenous estradiol on pulsatile LH release during the transition from infancy to the prepubertal period of development. Bull calves were assigned to treatments (N = 5 treatment) at 6 weeks of age. Treatments consisted of intact controls, castrates and castrates receiving estradiol implants. Plasma LH response was monitored over 8 hr periods at 7, 8, 9, 10, 11 and 13 weeks of age. Castration alone did not alter LH concentrations, compared to controls until 10 weeks of age. At 10, 11 and 13 weeks, mean LH concentration and the number of LH pulses/8 hr period were greater (P less than .05) in castrates than in controls. In castrates with estradiol implants, mean LH concentration and the number of LH pulses/8 hr period were suppressed at all ages compared to controls and castrate treatments. These results indicate that LH release is not inhibited by gonadal factors from 6 to 9 weeks of age in the bull calf. However, estradiol negative feedback on LH secretion is evident during this same developmental period.