Effects of dietary energy on sexual maturation and sperm production in Holstein bulls1

Abstract

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.

Plane of nutrition before and after 6 months of age in Holstein-Friesian bulls: I. Effects on performance, body composition, age at puberty, and postpubertal semen production

“…Although the response of age at puberty onset to early life dietary manipulation has been reported previously in bulls (Brito et al, 2007c;Dance et al, 2015;Harstine et al, 2015), this is the first study using dairy bulls to report that effects of a reduction in ADG during early life cannot be overcome through subsequent realimentation. In agreement with the findings of the current study, Brito et al (2007a) reported that the delay in puberty caused by restricting Angus and Angus × Charolais bulls from 10 to 26 wk could not be overcome by offering ad libitum concentrate after 26 wk of age, following a restricted diet (75% of the intake of ad libitum fed controls) in early life.…”

“…However, the reproductive potential of these young bulls is limited by the quantity and quality of semen that they can produce (Rawlings et al, 2008). Recent studies have reported that enhanced nutrition before 31 wk of age leads to earlier onset of puberty in Holstein-Friesian bulls (Dance et al, 2015;Harstine et al, 2015), whereas restricting the diet of beef bulls before 26 wk of age delays age at puberty onset, which could not be reversed by an increase in the plane of nutrition from 27 wk to 70 wk of age (Brito et al, 2007a). In both studies conducted on Holstein-Friesian bulls (Dance et al, 2015;Harstine et al, 2015), postpubertal semen production was unaffected by diet, whereas a high plane of nutrition from 10 to 30 wk in young beef bulls led to higher total daily sperm production at 74 wk of age compared with those offered a control diet from 10 to 74 wk of age (Brito et al, 2007b).…”

Long noncoding RNA expression profile changes associated with dietary energy in the sheep testis during sexual maturation

“…In previous studies, evidence indicated that nutrition can influence male reproduction. For example, Holstein bulls fed high-energy diet showed advanced testicular maturation 26 . In mature male sheep and goats, changes in feed intake can induce changes in the size of the seminiferous tubules and spermatogenic efficiency 1 .…”

Role of early life nutrition on the hypothalamic-pituitary-testicular axis of the bull

“…However, these bulls cannot produce ejaculates of sufficient quality for cryopreservation until they are greater than 1 year of age (Murphy et al 2018) and demand for their semen often far exceeds supply. Hastening the onset of puberty and subsequent sexual maturation would therefore benefit the industry and make high-quality semen available at a younger age (Harstine et al 2015).…”