Luteinizing hormone secretion before and after ovariectomy in prepubertal and pubertal beef heifers

The effects of sham ovariectomy (SOVX) or ovariectomy (OVX) on (1) basal luteinizing hormone (LH) concentrations, (2) number of LH peaks per hour and (3) magnitude of LH peaks were determined in prepubertal and pubertal beef heifers. Basal LH concentrations were not influenced by SOVX of prepubertal or pubertal heifers. However, after OVX, basal LH concentrations increased between 168 and 192 hr in prepubertal heifers and between 72 and 80 hr in pubertal heifers. The number of LH peaks per hour was not influenced by SOVX but OVX caused an increase in the number in both prepubertal and pubertal heifers, and the increase occurred sooner after OVX in pubertal than in prepubertal heifers. The magnitude of LH peaks was similar for both prepubertal and pubertal heifers prior to SOVX and OVX. Magnitude of LH peaks was unchanged after SOVX in prepubertal and pubertal heifers, but increased within the first 24 hr after OVX in pubertal heifers and within 168 to 192 hr after OVX in prepubertal heifers. These data indicate that inhibition of LH secretion by ovaries occurred in both prepubertal and pubertal beef heifers. The time-related differences between prepubertal and pubertal heifers in basal LH concentrations, number of LH peaks per hour and magnitude of the LH peaks after OVX may reflect a difference in endocrine environment in these two reproductive states. However, this hypothesis was not tested in this experiment.