Effects of treatment with LH or FSH from 4 to 8 weeks of age on the attainment of puberty in bull calves

A transient increase in gonadotropin secretion between 6 and 20 weeks of age is critical for the onset of puberty in bull calves. To try and hasten the onset of puberty, bull calves were treated (s.c.) with 3 mg of bLH (n=6) or 4 mg of bFSH (n=6) once every 2 days, from 4 to 8 weeks after birth; control calves received saline (n=6). At 4 and 8 weeks of age, mean LH concentrations were higher (P<0.05) in bLH-treated (2.3±0.04 ng/ml and 1.20±0.04 ng/ml) as compared to control calves (0.50±0.1 ng/ml and 0.70±0.10 ng/ml). Mean serum FSH concentrations at 4 and 8 weeks of age, were higher (P<0.05) in bFSH-treated (1.60±0.20 ng/ml and 1.10±0.2 ng/ml) as compared to control calves (0.38±0.07 ng/ml and 0.35±0.07 ng/ml). The age at which scrotal circumference (SC) first reached ≥28 cm, occurred earlier (P<0.05) in bFSH-treated calves as compared to saline-treated calves (39.3±1.3 and 44.8±1.3 weeks of age, respectively). Based on testicular histology at 56 weeks of age, treatment with bFSH resulted in greater (P<0.05) numbers of Sertoli cells (5±0.2, 6±0.3 and 5±0.3 in bLH-, bFSH- and saline-treated calves, respectively); elongated spermatids (42±2, 57±8 and 38±5 in bLH-, bFSH- and saline-treated calves, respectively) and spermatocytes (31±3, 38±3 and 29±2 in bLH-, bFSH- and saline-treated calves, respectively) per seminiferous tubule. We concluded that treatment of bull calves with bFSH from 4 to 8 weeks of age increased testicular growth (SC); hastened onset of puberty (SC≥28 cm); and enhanced spermatogenesis.