Plane of nutrition before and after 6 months of age in Holstein-Friesian bulls: II. Effects on metabolic and reproductive endocrinology and identification of physiological markers of puberty and sexual maturation

Abstract

The aim of this study was (1) to examine the effect of plane of nutrition during the first and second 6 mo of life on systemic concentrations of reproductive hormones and metabolites in Holstein-Friesian dairy bulls, and (2) to establish relationships with age at puberty and postpubertal semen production potential. Holstein-Friesian bull calves (n = 83) with a mean (standard deviation) age and body weight of 17 (4.4) d and 52 (6.2) kg, respectively, were assigned to a high or low plane of nutrition for the first 6 mo of life. At 24 wk of age, bulls were reassigned, within treatment, either to remain on the same diet or to switch to the opposite diet until puberty, resulting in 4 treatment groups: high-high, high-low, low-low, and low-high. Monthly blood samples were analyzed for metabolites (albumin, urea, total protein, β-hydroxybutyrate, glucose, nonesterified fatty acid, triglycerides and creatinine), insulin, insulin-like growth factor-1, leptin, adiponectin, FSH, and testosterone. A GnRH challenge was carried out at 16 and 32 wk of age (n = 9 bulls per treatment). Blood was collected at 15-min intervals for 165 min, with GnRH administered (0.05 mg/kg of body weight, i.v.) immediately after the third blood sample. Blood samples were subsequently analyzed for LH, FSH, and testosterone. Stepwise regression was used to detect growth and blood measurements to identify putative predictors of age at puberty and subsequent semen quality traits. Metabolic hormones and metabolites, in general, reflected metabolic status of bulls. Although FSH was unaffected by diet, it decreased with age both in monthly samples and following GnRH administration. Testosterone was greater in bulls on the high diet before and after 6 mo of age. Testosterone concentrations increased dramatically after 6 mo of age. Luteinizing hormone was unaffected by diet following GnRH administration but basal serum LH was greater in bulls on a high diet before 6 mo of age. In conclusion, the plane of nutrition offered before 6 mo of age influenced metabolic profiles, which are important for promoting GnRH pulsatility, in young bulls.

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

“…However, Lo-Hi bulls did not become fatter or have a greater muscle depth than bulls that were on a Hi diet pre-6 mo of age, highlighting the limited compensability of muscle and fat deposition in Holstein-Friesian bulls. Bulls on the Hi diet pre-6 mo had greater subcutaneous fat than Lo bulls at 6 mo, in line with the experimental design, suggesting that Hi bulls would have had greater fat and thus energy reserves when it is most important (early life), possibly leading to increased systemic concentrations of leptin (Byrne et al, 2018) which have been Values within row with different superscripts differ significantly.…”

Effect of Early Calf-Hood Nutrition on the Transcriptional Regulation of the Hypothalamic-Pituitary-Testicular axis in Holstein-Friesian Bull Calves

“…The animal model and management has previously been described by Byrne et al . 18 . Briefly, twenty Holstein-Friesian bull calves with a mean (±S.D.)…”

“…Blood samples were collected on a fortnightly basis to determine systemic concentrations of LH and was quantified by RIA as previously described by Byrne et al . 18 . Death was confirmed by exsanguination followed by decapitation.…”

Effect of early calf-hood nutrition on the transcriptomic profile of subcutaneous adipose tissue in Holstein-Friesian bulls

“…The advent of genomic selection in the dairy industry has resulted in the identification of sires for use in artificial insemination within weeks of birth and semen from these young bulls is in high demand once they reach puberty. Studies have shown that plane of nutrition in early calf-hood plays a critical role in the timing of the onset of puberty in bulls [ 1 – 3 ]. Recently, our research group has demonstrated that a high plane of nutrition prior to, but not after 6 months of age can accelerate puberty in Holstein-Friesian bulls by approximately 1 month [ 3 ].…”

“…Studies have shown that plane of nutrition in early calf-hood plays a critical role in the timing of the onset of puberty in bulls [ 1 – 3 ]. Recently, our research group has demonstrated that a high plane of nutrition prior to, but not after 6 months of age can accelerate puberty in Holstein-Friesian bulls by approximately 1 month [ 3 ]. This has been associated with the advancement of a transient rise in systemic concentrations of luteinising hormone (LH), which normally occurs between approximately 8 and 20 weeks of age [ 4 ].…”