LAUSR

The objective of this study was to examine the effect of nutrition during the first 18 weeks of life on the physiological and transcriptional functionality of the hypothalamic, anterior pituitary and testes in Holstein Friesian bull calves. Holstein Friesian bull calves with a mean (±S.D.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were assigned to either a HIGH (n=10) or LOW (n=10) plane of nutrition, to achieve an overall target growth rate of 1.2 or 0.5 kg/day, respectively. At 126±1.1 days of age, all calves were euthanised. Animal performance (weekly) and systemic concentrations of metabolic and reproductive hormones (at four week intervals) were assessed. Testicular histology, targeted gene and protein expression of the arcuate nucleus, anterior pituitary and testes were also assessed using qPCR and immunohistochemistry, respectively. Testicular tissue from post pubertal 19 month old Holstein Friesian bulls (n=10) that were reared under similar conditions was also available for comparative gene expression analysis. The metabolites and metabolic hormones generally reflected the improved metabolic status of the calves on HIGH bull calves (P<0.001). Only ghrelin receptor was upregulated in the anterior pituitary (P<0.05) and arcuate nucleus (P<0.10) in LOW compared to HIGH bull calves. Calves offered a high plane of nutrition were heavier at slaughter (P<0.001), had larger testes P<0.001), larger seminiferous tubule diameter P<0.001), more mature spermatogenic cells P<0.001) and more Sertoli cells (P<0.05) in accordance with both morphological and transcriptional data. This study indicates that a high plane of nutrition during early calf-hood alters gene expression which advances testicular development and hastens spermatogenesis.