Heat stress and seasonal effects on reproduction in the dairy cow - a review
Heat stress and seasonal effects on reproduction in the dairy cow - a review
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DOI：
10.1016/s0093-691x(03)00126-2
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发表时间：
2003-10-01
期刊：
影响因子：
2.8
通讯作者：
Scaramuzzi, RJ
中科院分区：
文献类型：
--
作者：
De Rensis, F;Scaramuzzi, RJ
在一年中炎热的月份受精的奶牛，生育能力会下降。不同的因素导致这种情况;最重要的是温度和湿度增加的结果，导致明显的发情表现减少，食欲和干物质摄入减少。热应激降低了所选卵泡的优势程度，这可以被看作是卵泡膜和颗粒细胞类固醇生成能力的降低以及血液雌二醇浓度的下降。血浆孕酮水平可以增加或减少，这取决于热应激是急性还是慢性，以及动物的代谢状态。这些内分泌变化降低了卵泡活性，改变了排卵机制，导致卵母细胞和胚胎质量下降。子宫环境也被改变，降低了胚胎植入的可能性。热应激会降低食欲和干物质摄入量，从而延长产后能量负平衡期，并延长产犊-受孕间隔，特别是在高产奶牛中。冷却系统的使用可能对生育力有有益的影响，但以这种方式冷却的奶牛仍然无法与冬季实现的生育力相匹配。最近的研究表明，使用促性腺激素诱导卵泡发育和排卵可以降低奶牛季节性产后不孕症的严重程度。(C)2003年爱思唯尔科学公司All rights reserved.
In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations. Plasma progesterone levels can be increased or decreased depending on whether the heat stress is acute or chronic, and on the metabolic state of the animal. These endocrine changes reduce follicular activity and alter the ovulatory mechanism, leading to a decrease in oocyte and embryo quality. The uterine environment is also modified, reducing the likelihood of embryo implantation. Appetite and dry matter intake are both reduced by heat stress thus prolonging the postpartum period of negative energy balance and increasing the calving-conception interval, particularly in high producing dairy cows. The utilization of cooling systems may have a beneficial effect on fertility but dairy cows cooled in this way are still unable to match the fertility achieved in winter. Recent studies suggest that the use of gonadotropins to induce follicular development and ovulation can decrease the severity of seasonal postpartum infertility in dairy cows. (C) 2003 Elsevier Science Inc. All rights reserved.