Dance Alysha, Thundathil Jacob, Wilde Randy, Blondin Patrick, Kastelic John
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada.
Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, AB T1J 4B1, Canada.
J Dairy Sci. 2015 Feb;98(2):987-98. doi: 10.3168/jds.2014-8564. Epub 2014 Dec 12.
Holstein bull calves often reach artificial insemination centers in suboptimal body condition. Early-life nutrition is reported to increase reproductive performance in beef bulls. The objective was to determine whether early-life nutrition in Holstein bulls had effects similar to those reported in beef bulls. Twenty-six Holstein bull calves were randomly allocated into 3 groups at approximately 1 wk of age to receive a low-, medium-, or high-nutrition diet, based on levels of energy and protein, from 2 to 31 wk of age. Calves were on their respective diets until 31 wk of age, after which they were all fed a medium-nutrition diet. To evaluate secretion profiles and concentrations of blood hormones, a subset of bulls was subjected to intensive blood sampling every 4 wk from 11 to 31 wk of age. Testes of all bulls were measured once a month; once scrotal circumference reached 26cm, semen collection was attempted (by electroejaculation) every 2 wk to confirm puberty. Bulls were maintained until approximately 72 wk of age and then slaughtered at a local abattoir. Testes were recovered and weighed. Bulls fed the high-nutrition diet were younger at puberty (high=324.3 d, low=369.3 d) and had larger testes for the entire experimental period than bulls fed the low-nutrition diet. Bulls fed the high-nutrition diet also had an earlier and more substantial early rise in LH than those fed the low-nutrition diet and had increased concentrations of insulin-like growth factor-I (IGF-I) earlier than the bulls fed the low-nutrition diet. Furthermore, we detected a temporal association between increased IGF-I concentrations and an early LH rise in bulls fed the high-nutrition diet. Therefore, we inferred that IGF-I had a role in regulating the early gonadotropin rise (in particular, LH) and thus reproductive development of Holstein bulls. Overall, these results support our hypothesis that Holstein bull calves fed a high-nutrition diet reach puberty earlier and have larger testes than those fed a low-nutrition diet, and they provide clear evidence that nutritional modulation of Holstein bull calves during early life has profound effects on reproductive development.
荷斯坦公牛犊往往在身体状况欠佳时进入人工授精中心。据报道，早期营养可提高肉用公牛的繁殖性能。本研究的目的是确定荷斯坦公牛的早期营养是否具有与肉用公牛类似的效果。26头荷斯坦公牛犊在约1周龄时被随机分为3组，从2周龄至31周龄，根据能量和蛋白质水平分别饲喂低、中、高营养日粮。犊牛在31周龄前一直食用各自的日粮，之后全部改为中等营养日粮。为评估血液激素的分泌情况和浓度，从11周龄至31周龄，每隔4周对一部分公牛进行密集采血。所有公牛的睾丸每月测量一次；一旦阴囊周长达到26厘米，每2周尝试（通过电刺激采精）采集精液以确认青春期。公牛饲养至约72周龄，然后在当地屠宰场屠宰。取出睾丸并称重。与饲喂低营养日粮的公牛相比，饲喂高营养日粮的公牛青春期来得更早（高营养组=324.3天，低营养组=369.3天），且在整个实验期间睾丸更大。与饲喂低营养日粮的公牛相比，饲喂高营养日粮的公牛促黄体生成素（LH）的早期升高更早且幅度更大，胰岛素样生长因子-I（IGF-I）的浓度升高也比饲喂低营养日粮的公牛更早。此外，我们在饲喂高营养日粮的公牛中检测到IGF-I浓度升高与LH早期升高之间存在时间关联。因此，我们推断IGF-I在调节早期促性腺激素升高（特别是LH）以及荷斯坦公牛的生殖发育中发挥作用。总体而言，这些结果支持了我们的假设，即饲喂高营养日粮的荷斯坦公牛犊比饲喂低营养日粮的公牛犊青春期来得更早且睾丸更大，并且它们提供了明确的证据，表明荷斯坦公牛犊在生命早期的营养调节对生殖发育具有深远影响。
