HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Amann, R. P. Search for Related Content PubMed PubMed Citation Articles by Amann, R. P.

Endocrine Changes Associated with Onset of Spermatogenesis in Holstein Bulls¹

Animal Reproduction Laboratory, Colorado State University, Fort Collins 80523

ABSTRACT

After birth, a bull enters a period of infancy during which the reproductive organs are relatively quiescent. This is followed by the prepubertal period, which starts at 10 to 12 wk in well-fed Holstein bulls, characterized by profound changes of hypothalamic, pituitary, and gonadal function that culminate in puberty. The prepubertal sequence of events probably is: a) initiation of spontaneous discharge of luteinizing hormone; b) hormone induced differentiation of Leydig cells with increased secretion of androstenedione in response to luteinizing hormone stimulation; c) further differentiation of Leydig cells resulting in luteinizing hormone-stimulated secretion of testosterone; d) testosterone-induced differentiation of indifferent supporting cells to Sertoli cells concomitant with testosterone-induced differentiation of gonocytes to prespermatogonia and Aspermatogonia; e) increased sensitivity of the hypothalamus-anterior pituitary to negative feedback of gonadal steroids; f) diminished frequency and amplitude of luteinizing hormone discharge; g) formation of junctional complexes between Sertoli cells and establishment of the bood-testis barrier; h) formation of primary spermatocytes and ultimately spermatids and spermatozoa; and i) continued increase of efficiency of spermatogenesis until sufficient sperm are produced to provide the first ejaculum around 37 to 38 wk. Following puberty, the reproductive capacity of a bull increases for several years until the male is sexually mature.

¹ Research by the author was supported by the Pennsylvania Agricultural Experiment Station and by the Animal Reproduction Laboratory, Colorado State University.

This article has been cited by other articles:

				E T Bagu, S Cook, C L Gratton, and N C Rawlings Postnatal changes in testicular gonadotropin receptors, serum gonadotropin, and testosterone concentrations and functional development of the testes in bulls. Reproduction, September 1, 2006; 132(3): 403 - 411. [Abstract] [Full Text] [PDF]