This study examined the effect of plane of nutrition on the endocrinological regulation of the hypothalamic pituitary- ovarian (HPO) axis in beef heifer calves during a critical sexual developmental window early in calf hood. Forty Holstein-Friesian × Angus heifers (mean age 19 days, SEM = 0.63) were assigned to a high (HI; ADG 1.2 kg) or moderate (MOD; ADG 0.50 kg) nutritional level from 3 to 21 wk of life. Intake was recorded using an electronic calf feeding system, BW was recorded weekly, and blood samples were collected on wk of age 5, 10, 15 and 20 for metabolite, reproductive and metabolic hormone determination. At 19 wk of age, on sequential days an 8 h window bleed was carried out for luteinising hormone (LH), follicle stimulating hormone (FSH) and estradiol analysis. To characterize anterior pituitary gland function an intravenous GnRH challenge was conducted (19 wk of age). Blood was collected via jugular cathether every 15 min for 135 min for analysis of LH, FSH and estradiol. Calves were subsequently euthanized at 21 wk of age the anterior pituitary, metabolic organs and reproductive tract were weighed, and ovarian surface follicular numbers and oocytes recovered were recorded. Mean ADG was 1.18 kg and 0.50 kg for HI and MOD, respectively, resulting in a 76.6 kg difference in BW (P < 0.001). Blood insulin, glucose and IGF-1 concentrations were greater (P < 0.001) for HI compared with MOD. There was a diet × time interaction for leptin (P < 0.01); concentrations were greater in HI compared with MOD at 20 wk of age with no difference between treatments before this. Dietary treatment did not alter concentrations of adiponectin or anti-mullerian hormone (AMH). There was a diet × time interaction for FSH, whereby MOD had greater concentrations than HI at 10, 15 and 20, but not at 5 wk of age. Over the duration of an 8 h window bleed (19 wk of age) serum concentrations of LH, LH pulse frequency and amplitude were unaffected by treatment, whereas FSH (0.23 v 0.43 ng/ml) and estradiol (0.53 v 0.38 ng/ml) concentrations were less than and greater, respectively, for HI than MOD (P < 0.05). Likewise, following a GnRH challenge, area under the curve (AUC) analysis revealed greater (P < 0.01) estradiol and lesser (P < 0.01) FSH concentrations in calves on the HI relative to MOD diet, whereas concentrations of LH were unaffected (P = 0.26) between treatments. Ovarian surface follicle numbers were greater (P < 0.05) in HI compared with MOD. Total reproductive tract, uterus and ovarian tissue expressed relative to BW were greater (P < 0.05) for HI compared with MOD. In conclusion, enhanced nutrition in early calfhood advances the ontogeny development of the HPO axis.

中文翻译：

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犊牛营养对小牛犊的代谢激素、促性腺激素和雌二醇浓度以及生殖器官发育的影响。

本研究检查了营养水平对小牛犊牛下丘脑垂体 - 卵巢 (HPO) 轴内分泌调节的影响，在犊牛头罩早期的关键性发育窗口期间。40 头荷斯坦 - 弗里斯兰 × 安格斯小母牛（平均年龄 19 天，SEM = 0.63）被分配到高（HI；ADG 1.2 kg）或中等（MOD；ADG 0.50 kg）营养水平，从 3 周到 21 周。使用电子犊牛饲喂系统记录摄入量，每周记录体重，并在 5、10、15 和 20 周龄时收集血样用于代谢物、生殖和代谢激素的测定。在 19 周龄时，连续几天进行 8 小时窗口出血以进行黄体生成素 (LH)、促卵泡激素 (FSH) 和雌二醇分析。为了表征垂体前叶的功能，进行了静脉注射 GnRH 攻击（19 周龄）。每 15 分钟通过颈静脉导管收集血液，持续 135 分钟，用于分析 LH、FSH 和雌二醇。随后在 21 周龄时对小牛实施安乐死，称重垂体前叶、代谢器官和生殖道，并记录卵巢表面的卵泡数和卵母细胞。HI 和 MOD 的平均 ADG 分别为 1.18 kg 和 0.50 kg，导致体重相差 76.6 kg（记录卵巢表面卵泡数和回收的卵母细胞。HI 和 MOD 的平均 ADG 分别为 1.18 kg 和 0.50 kg，导致体重相差 76.6 kg（记录卵巢表面卵泡数和回收的卵母细胞。HI 和 MOD 的平均 ADG 分别为 1.18 kg 和 0.50 kg，导致体重相差 76.6 kg（P < 0.001)。与 MOD 相比，HI 的血胰岛素、葡萄糖和 IGF-1 浓度更高（P < 0.001）。瘦素存在饮食×时间交互作用（P < 0.01）；与 MOD 相比，在 20 周龄时 HI 中的浓度更高，在此之前的处理之间没有差异。饮食治疗并未改变脂联素或抗苗勒管激素 ( AMH) 的浓度）。FSH 存在饮食×时间相互作用，其中 MOD 在 10、15 和 20 岁时的浓度高于 HI，但在 5 周龄时没有。在 8 小时窗口出血（19 周龄）的持续时间内，LH、LH 脉冲频率和振幅的血清浓度不受治疗影响，而 FSH（0.23 v 0.43 ng/ml）和雌二醇（0.53 v 0.38 ng/ml） HI 的浓度分别小于和大于 MOD（P < 0.05）。同样，在 GnRH 激发后，曲线下面积 (AUC) 分析显示，相对于 MOD 饮食，HI 组犊牛的 FSH 浓度更高（P < 0.01），FSH 浓度更低（P < 0.01），而 LH 浓度不受影响（P= 0.26) 处理之间。与 MOD 相比，HI 中的卵巢表面卵泡数更多（P < 0.05）。与 MOD 相比，HI 的总生殖道、子宫和卵巢组织表达相对于 BW 更大（P < 0.05）。总之，犊牛早期营养增强促进了 HPO 轴的个体发育。