In the current context of climate change, livestock production faces many challenges to improve the sustainability of systems. Dairy farming, in particular, must find ways to select animals that will be able to achieve sufficient overall production while maintaining their reproductive ability in environments with increasing temperatures. With future forecasted climate conditions in mind, this study used data from Holstein and Montbeliarde dairy cattle to: (1) estimate the genetic-by-temperature-humidity index (THI) interactions for female fertility, and (2) evaluate the production-fertility trade-off with increasing values of THI. Two-trait random regression models were fitted for conception rate (fertility) and test-day protein yield (production). For fertility, genetic correlations between different THI values were generally above 0.75, suggesting weak genotype-by-THI interactions for conception rate in both breeds. However, the genetic correlations between the conception rate breeding values at the current average THI (THI = 50, corresponding to a 24-h average temperature of 8 °C at 50% relative humidity) and their slopes (i.e., potential reranking) for heat stress scenarios (THI > 70), were different for each breed. For Montbeliarde, this correlation tended to be positive (i.e., overall the best reproducers are less affected by heat stress), whereas for Holstein it was approximately zero. Finally, our results indicated a weak antagonism between production and fertility, although for Montbeliarde this antagonism intensified with increasing THI. Within the range of weather conditions studied, increasing temperatures are not expected to exacerbate the fertility-production trade-off. However, our results indicated that the animals with the best breeding values for production today will be the most affected by temperature increases, both in terms of fertility and production. Nonetheless, these animals should remain among the most productive ones during heat waves. For Montbeliarde, the current selection program for fertility seems to be adequate for ensuring the adaptation of fertility traits to temperature increases, without adverse effects on production. Such a conclusion cannot be drawn for Holstein. In the future, the incorporation of a heat tolerance index into dairy cattle breeding programs would be valuable to promote the selection of animals adapted to future climate conditions.

中文翻译：

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温湿度指数对奶牛生育力与生产权衡演化的影响


在当前气候变化的背景下，畜牧业生产面临着提高系统可持续性的许多挑战。尤其是奶牛养殖业，必须找到方法来选择能够实现足够的总体产量，同时在温度升高的环境中保持繁殖能力的动物。考虑到未来预测的气候条件，本研究使用荷斯坦奶牛和蒙贝利亚德奶牛的数据来：（1）估计雌性生育力的遗传-温度-湿度指数（THI）相互作用，以及（2）评估生产-生育力与 THI 值的增加进行权衡。针对受孕率（生育力）和测试日蛋白质产量（产量）拟合了双性状随机回归模型。对于生育力，不同 THI 值之间的遗传相关性通常高于 0.75，表明两个品种的受孕率之间的基因型与 THI 相互作用较弱。然而，当前平均 THI（THI = 50，对应于 50% 相对湿度下 8 °C 的 24 小时平均温度）下的受孕率育种值与其热斜率（即潜在的重新排名）之间的遗传相关性每个品种的压力情景（THI > 70）都不同。对于蒙贝利亚德来说，这种相关性往往是正的（即，总体而言，最好的繁殖者受热应激的影响较小），而对于荷斯坦来说，这种相关性大约为零。最后，我们的结果表明产量和生育力之间存在微弱的拮抗作用，尽管对于蒙贝利亚德来说，这种拮抗作用随着 THI 的增加而加剧。在研究的天气条件范围内，气温升高预计不会加剧生育力与生产之间的权衡。 然而，我们的结果表明，当今具有最佳育种生产价值的动物在生育力和产量方面将受到温度升高的最大影响。尽管如此，这些动物在热浪期间仍应是生产力最高的动物之一。对于蒙贝利亚德来说，目前的生育力选择计划似乎足以确保生育性状适应温度升高，而不会对生产产生不利影响。对于荷斯坦牛来说，不能得出这样的结论。未来，将耐热指数纳入奶牛育种计划对于促进选择适应未来气候条件的动物具有重要意义。