Responsiveness of prepubertal crossbred bull calves to exogenous GnRH and its impact on reproductive hormones under tropical conditions

Abstract

This study investigated the age related variations in luteinizing hormone (LH), androstenedione, testosterone, and total estrogens response to exogenous gonadotropin-releasing hormone (GnRH) in Holstein–Friesian (HF) × Tharparkar bull calves. Fifteen bull calves were selected and, based on their age, were divided into Group I (14–16 months, n = 5), Group II (9–12 months, n = 5), and Group III (6–8 months, n = 5). All bull calves were administered with 10 µg of GnRH intramuscularly. Blood samples were collected at an interval of 30 min commencing 1 h prior to GnRH treatment until 4 h post-GnRH treatment and thereafter, at an interval of 1 h for the next 3 h. Endocrine response in terms of pretreatment values, peak values, area under curve, and time taken to attain peak values for LH, androstenedione, testosterone, and total estrogens was evaluated in all the bull calves. Significant differences were observed in pretreatment values, peak concentrations, and area under curve for androstenedione and testosterone between the groups; with response being higher in Group I bull calves. The results indicated that the HF × Tharparkar bull calves of 14 months age and above respond to exogenous GnRH by secreting significant amounts of testosterone.

Influence of Testosterone on Body and Testicular Development in Zebu Cattle in the Tropical Climate

“…The serum testosterone differed (P < 0.05) between 10 and 12 months ( Table 5), preceding a significant increase in morphological variables. At 12 months of age, the serum testosterone concentration in Brahman males was similar to that found in Nellore cattle aged 31 and 35 months by [37], and in crossbred Holstein × Thaparkar males between 9 and 12 months of age by [3]. In the present study, Brahman males produced similar levels of testosterone at younger ages than Zebus [37], and in the same age group as crossbred cattle [3], revealing sexual precocity.…”

“…However, there was no difference (P > 0.05) between 10 and 12 months of age for the scrotal circumference. Sexual precocity is more related to body weight than to the chronological age of bovines; thus, the analysis of several morphometric characteristics is important to guide Advances in Testosterone Action the selection for genetic improvement purposes [1,3,19]. Sexual precocity was described in Nellore cattle aged between 500 and 580 days and between 620 and 740 days of age [8].…”

“…The study of puberty in young zebus is of great importance, due to selection of sexually precocious (i.e. below the average herd age) future breeders [3]. In Bos indicus, puberty usually occurs between the ages of 16 and 18 months [4,5], but these males are seldom used for breeding purposes before the age of 2 [6,7].…”