Effect of implanting bull calves with testosterone propionate, dihydrotestosterone propionate or oestradiol-17  prepubertally on the pituitary-testicular axis and on postpubertal social and sexual behaviour

Abstract

Twelve non-implanted crossbred bull calves served as controls and 30 crossbred bull calves (10/treatment) were implanted for 82 days, beginning at 34 days of age, to determine the influence of testosterone propionate (TP), dihydrotestosterone propionate (DHTP) and oestradiol-17 beta (E2) on prepubertal and pubertal pituitary-testicular function and on postpubertal social and sexual behaviour. Compared with control bulls, concentrations of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and inhibin concentrations were suppressed (P less than 0.01) in all implanted bulls. Testosterone (T) concentration increased (P less than 0.001) in TP-implanted, but decreased (P less than 0.01) in DHTP and E2 bulls during the implant period. LH response to gonadotrophin-releasing hormone (GnRH) challenge during the implant period (2.5 months of age) was less (P less than 0.01) in TP, E2 and DHTP bulls than in controls. A small but significant T response to GnRH occurred in control bulls at 2.5 months of age. LH and T responses to GnRH challenge at 7 months of age (100 days after implant removal) was similar (P greater than 0.20) in control and implanted bulls. Steroid implants administered prepubertally had no effect (P greater than 0.10) on postpubertal social and sexual behaviours, including number of flehmen responses, abortive mounts, services and competitive order score. Body weight did not differ (P greater than 0.10) between treatment groups, but testis size was reduced (P less than 0.01) during the implant period and up to 10 months of age in treated bulls compared with controls. Testes remained smaller in E2-treated bulls up to the end of the study (23 months of age), but daily sperm production and epididymal weight did not differ (P greater than 0.10) between treatment groups at slaughter. Control bulls reached puberty earlier (P less than 0.01; 270 +/- 11 days of age) than did TP (302 +/- 11 days), DHTP (309 +/- 11 days) or E2 (327 +/- 11 days) bulls. Although puberty was delayed in all implant groups, there was no difference in scrotal circumference at puberty (average 28.4 +/- 0.4 cm) between treatment groups. Our findings indicate that TP, DHTP and E2 implants administered prepubertally result in acute suppression of serum LH, FSH and inhibin during the implant period and in post-implant suppression of testis size and delayed puberty in bulls. The lack of treatment effect on behaviour suggests that steroidal programming of sexual behaviour occurs before 1 month of age in bulls.

Growth and pubertal development in Brahman-, Boran-, Tuli-, Belgian Blue-, Hereford- and Angus-sired F1 bulls

“…Regardless of sire breed, bulls reached puberty when scrotal circumference reached approximately 28 cm, and PTV reached approximately 300 cm 3 . We have shown previously that Zebu × Bos taurus bulls and bulls of Bos taurus beef breeds reach puberty at 28 cm scrotal circumference (Lunstra et al, 1978(Lunstra et al, , 1988(Lunstra et al, , 1993Godfrey et al, 1992). Consistent with the present results, other researchers have reported that Brahman-, Romosinuano-, Nellore-, Senepol-, and Tuli-sired bulls reach puberty at 27 to 31 cm scrotal circumference (Chase et al, 1997(Chase et al, , 2001).…”

Evaluation of sexual behavior of hair sheep rams in a tropical environment.

“…Other studies have shown that bulls exhibit an increase in level of sexual behavior over time also (Godfrey and Lunstra, 1989;Godfrey et al, 1992). Price et al (1991a) have shown that a brief exposure of young, virgin rams to estrous ewes can increase their level of sexual behavior to a level similar to that of experienced rams.…”

Sexual Maturation in the Bull

“…Testosterone and dihydrotestosterone suppress serum concentrations of LH and FSH in bull calves between 4 and 20 weeks of age (Kennedy et al. 1985; Godfrey et al. 1992).…”