EFFECTS OF TREATMENT WITH LH RELEASING HORMONE BEFORE THE EARLY INCREASE IN LH-SECRETION ON ENDOCRINE AND REPRODUCTIVE DEVELOPMENT IN BULL CALVES

Between 6 and 20 weeks of age an early increase in LH secretion has be en reported in Hereford bull calves. Delaying this early increase in L H secretion delays testicular development. This study was designed to determine whether a premature increase in LH secretion during the earl y postnatal period enhances testicular development. Ten age-and body w eight-matched Hereford bull calves were divided into two groups. One g roup (n = 5) received 200 ng LH releasing hormone (LHRH) i.v. every 2 h for 14 days, between 4 and 6 weeks of age. On the basis of blood sam ples taken every 15 min for 10 h, mean serum LH and testosterone conce ntrations and LH pulse frequency were increased by LHRH treatment (P<0 .05). Serum concentrations of FSH were not significantly influenced by treatment (P>0.05). In treated animals at 24 weeks of age, mean serum testosterone concentrations and LH pulse amplitude were increased (P< 0.05). The concentrations of spermatozoa in electroejeculates collecte d at 52 weeks of age were greater in LHRH-treated compared with contro l calves. Testicular growth was enhanced by LHRH treatment and histolo gical evaluation of the testis at 54 weeks of age showed increased spe rmatogenesis and also larger numbers of Sertoli cells per tubule cross -section as a result of LHRH treatment. We conclude that treatment wit h LHRH before the early increase in LH secretion altered testicular de velopment and suggest that the early increase in LH secretion in bull calves may be critical for initiating and regulating the progression o f reproductive maturation.