Animal and Bioscience Research Department, Teagasc Grange, Dunsany, Co. Meath, Ireland; School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
Laboratory of Animal Reproduction, Department of Biological Sciences, University of Limerick, Limerick, Ireland.
Theriogenology. 2017 Jul 1;96:58-68. doi: 10.1016/j.theriogenology.2017.04.002. Epub 2017 Apr 3.
The onset of puberty in the bull is regulated by the timing of early GnRH pulsatility release from the hypothalamus, which has been demonstrated to be affected by plane of nutrition during calf-hood. The aim of this study was to determine the effect of plane of nutrition on growth rate, scrotal development, metabolite concentrations and exogenous gonadotrophin (GnRH) induced release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone (TT) in pre-pubertal bulls of two contrasting dairy breeds. Holstein-Friesian and Jersey bull calves were assigned to either a high or low plane of nutrition from 3 to 49 weeks of age. Intensive blood sampling was conducted at 16, 24 and 32 weeks of age, every 15 min from 30 min prior to intravenous administration of exogenous GnRH to 135 min after. Monthly blood samples were also collected and analyzed for insulin like growth factor 1 (IGF-1), insulin, leptin, adiponectin and metabolite concentration. Insulin and IGF-1 were higher in bulls on a high plane of nutrition (P < 0.001) but were not affected by breed (P > 0.05). Leptin was not affected by plane of nutrition or breed (P > 0.05). Adiponectin tended to be higher in bulls on a high plane of nutrition (P = 0.05), but was not affected by breed (P > 0.05). Bulls on a high plane of nutrition had a greater concentration of LH in response to GnRH (P < 0.05) but there was no effect of breed (P > 0.05). FSH concentration was not influenced by breed or plane of nutrition but FSH concentrations did decrease with age (P < 0.01), while, LH was not affected by age (P > 0.05). Jersey bulls, particularly those on a high plane of nutrition, had higher TT production in the pre-pubertal period (P < 0.001). Using 28 cm as a proxy for age at puberty, bulls on a high plane of nutrition were predicted to reach puberty earlier than bulls on a low plane. In conclusion, the data clearly demonstrate that a high plane of nutrition positively affects several key nutritional and reproductive hormones which are critical to the endocrinological functionality of the hypothalamic-pituitary-testicular axis in dairy-bred bull calves.
公牛的青春期起始受下丘脑 GnRH 脉冲释放时间的调控，而这一过程受到牛犊期营养水平的影响。本研究旨在确定营养水平对两个不同奶牛品种（荷斯坦-弗里生和泽西）的未成熟公牛生长速度、阴囊发育、代谢物浓度以及外源性促性腺激素（GnRH）诱导的促黄体生成素（LH）、促卵泡激素（FSH）和睾酮（TT）释放的影响。荷斯坦-弗里生和泽西公牛犊从 3 至 49 周龄时分别接受高或低营养水平饲养。16、24 和 32 周龄时进行密集采血，从静脉注射外源性 GnRH 前 30 分钟开始，每 15 分钟采一次血，持续 135 分钟。每月采集血液样本并分析胰岛素样生长因子 1（IGF-1）、胰岛素、瘦素、脂联素和代谢物浓度。高营养水平组的公牛胰岛素和 IGF-1 水平更高（P<0.001），但不受品种影响（P>0.05）。瘦素不受营养水平或品种影响（P>0.05）。脂联素在高营养水平组的公牛中趋于更高（P=0.05），但不受品种影响（P>0.05）。高营养水平组的公牛对 GnRH 的 LH 反应更大（P<0.05），但不受品种影响（P>0.05）。FSH 浓度不受品种或营养水平影响，但随着年龄的增长而降低（P<0.01），而 LH 不受年龄影响（P>0.05）。泽西公牛，尤其是高营养水平组的公牛，在青春期前的 TT 产量更高（P<0.001）。使用 28cm 作为青春期年龄的替代指标，高营养水平组的公牛预计比低营养水平组的公牛更早达到青春期。总之，数据清楚地表明，高营养水平对几个关键的营养和生殖激素产生积极影响，这些激素对奶牛品种公牛下丘脑-垂体-睾丸轴的内分泌功能至关重要。
