奶牛不排卵状况的研究综述

卵泡生长可分为三个阶段：卵泡出现；卵泡的选择优势化与闭锁分离；卵泡排卵。不排卵的情况可分为：①生长卵泡不能生长至“分离期”。原因可能是极度的营养缺乏。②卵泡可生长到“分离期”，但没有达到排卵体积。这方面研究得较多，认为这类牛比正常牛有更强的E2对GnRH／LH的负反馈，在营养不良或吮乳时可引起这类不排卵状况。③卵泡生长的最终体积大于排卵卵泡，这类牛的特征是下丘脑对E2的正反馈作用不敏感；高产奶牛常见。对于第一种情况，关键在于预防，提高育成期的饲管水平。后两种常见的不排卵状况是由于下丘脑对E2反应的敏感性改变；常用增加血液循环中P4的浓度改变GnRH／LH释放的脉冲以协助卵泡最后阶段的生长，或重新建立下丘脑对E2的正反馈来治疗。

The Studies of Anovulatory Conditions in Dairy Cows

Three critical stages are proposed by the final stages of follicular growth as follows: emergence, deviation, and ovulation. Anovulatory conditions on the basis of these three points can be classified as the following three types. First, there is a growth of follicles to emergence but not to deviation stage. However, there are relatively few scientific investigations on this condition. The reason may be due to the extremely undernutrition. Second, follicles can grow to deviation stage but not to ovulatory size, which has been extensively studied. It is characterized by a greater negative feedback effect of estradiol on GnRH/LH pulses than found in normally cycling cows. Undernutrition or suckling can cause this anovulatory condition. Third, the follicles grow larger than ovulatory size. It is common in high producing lactating dairy cows. This condition is characterized by an insensitivity of the hypothalamus to the positive feedback effects of estradiol. For the first condition, there is not a suitable treatment. Providing cows with good nutrition can prevent it. Since the last two anovulatory conditions are due to the changes in the responsiveness of hypothalamus to estradiol, now, it is very common as treatments to increase circulating progesterone concentration so that to alter GnRH/LH pulses and help the follicles grow in their final stages, or to reset the hypothalamic responsiveness to the positive feedback effects of estradiol.