Montgomery G W, Scott I C, Hudson N
J Reprod Fertil. 1985 Jan;73(1):45-50. doi: 10.1530/jrf.0.0730045.
Angus cows were first mated at approximately 27 months of age in 2 herds, calving 21 July to 15 September (Group E) or 9 September to 30 October (Group L). The cows were fed a high (H) or medium (M) plane of nutrition for 55 days before and 40 days after calving. There was a mean liveweight difference of 35 kg between cows in Groups EH + LH and Groups EM + LM immediately after calving and at 40 days after calving. Immediately after calving cows in Groups EH + EM were 11 kg heavier than cows in Groups LH + LM, but there was no difference at 40 days after calving. There was a significant interaction between calving time and nutrition in the return of cyclic ovarian function assessed from both interval to first oestrus and first elevated progesterone concentration. Mean intervals from calving to first oestrus were 66.7, 82.7, 56.7 and 62.3 days in Groups EH, EM, LH and LM respectively. These data demonstrate that season of calving influences resumption of ovarian cycles even at a constant high plane of nutrition and that season of calving interacts with nutrition such that effects of season are more likely to be expressed under conditions of low nutrition.
在两个牛群中，安格斯母牛首次配种时年龄约为27个月，产犊时间为7月21日至9月15日（E组）或9月9日至10月30日（L组）。母牛在产犊前55天和产犊后40天被饲喂高（H）或中等（M）营养水平的饲料。产犊后立即以及产犊后40天时，EH组 + LH组的母牛与EM组 + LM组的母牛平均活重相差35千克。产犊后立即，EH组 + EM组的母牛比LH组 + LM组的母牛重11千克，但在产犊后40天时没有差异。从首次发情间隔和首次孕酮浓度升高来评估，产犊时间和营养在周期性卵巢功能恢复方面存在显著交互作用。EH组、EM组、LH组和LM组从产犊到首次发情的平均间隔分别为66.7天、82.7天、56.7天和62.3天。这些数据表明，即使在恒定的高营养水平下，产犊季节也会影响卵巢周期的恢复，并且产犊季节与营养相互作用，使得季节效应在低营养条件下更有可能表现出来。
