Effects of dietary energy on sexual maturation and sperm production in Holstein bulls.

In prepubertal bulls and heifers of dairy and beef breeds, puberty can be induced to occur earlier than typical with targeted high-energy diets due to precocious activation of the endocrine mechanisms that regulate puberty. Precocious activation of puberty in bulls intended for use in the AI industry has the potential to hasten and perhaps increase sperm production. It was hypothesized that feeding bulls a high-energy diet beginning at 8 wk of age would advance the prepubertal rise in LH and lead to advanced testicular maturation and age at puberty. From 58 to 230 ± 0.3 d of age, Holstein bulls received either a high-energy diet (HE;n = 9; targeted ADG 1.5 kg/d) or a control diet (CONT;n = 10; targeted ADG 0.75 kg/d). Thereafter, all bulls were fed a similar diet. The HE treatment increased LH secretion at 125 d of age, testosterone concentrations from 181 to 210 d, and scrotal circumference (SC) from 146 to 360 d of age relative to the CONT treatment. Beginning at 241 ± 5 d of age, semen collection (artificial vagina) was attempted every 14 d in bulls from the HE (n = 8) and CONT (n = 7) treatment until each bull attained puberty (ejaculate containing 50 × 10 spermatozoa with 10% motility). To assess semen production as mature bulls, semen was collected thrice weekly beginning at 541 ± 5 d of age until slaughter at 569 ± 5 d of age. After slaughter, epididymal and testicular measurements were collected and testicular tissue was fixed to determine seminiferous tubule diameter. Age at puberty did not differ between treatments (310 ± 35 d). Although testis and epididymal weight and testis volume were greater (P < 0.05) in the HE than the CONT treatment, sperm production of mature bulls did not differ between treatments. Diameter of seminiferous tubules also did not differ between treatments. We conclude that the HE advanced aspects of sexual maturation and increased testes size, but this was not reflected in hastened puberty or sperm production in the present experiment.