García-Ispierto I, López-Gatius F, Bech-Sabat G, Santolaria P, Yániz J L, Nogareda C, De Rensis F, López-Béjar M
Department of Animal Health and Anatomy, Autonomous University of Barcelona, Barcelona, Spain.
Theriogenology. 2007 May;67(8):1379-85. doi: 10.1016/j.theriogenology.2007.02.009. Epub 2007 Apr 6.
Summer heat stress is a main factor related to low conception rate in high producing dairy herds in warm areas worldwide. We assessed the impact of several climate variables on conception rate in high producing dairy cows in northeastern Spain by examining 10,964 inseminations. The temperature-humidity index (THI) was compared with maximum temperature in terms of its efficiency at predicting conception rate. The following data were recorded for each animal: herd, lactation number, insemination number, insemination date, inseminating bull, and AI technician along with climate variables such as mean and maximum temperatures, rainfall, mean and maximum THI for individual time points Days 7 to 1 before insemination, the day of insemination and 1, 2 and 3 days after insemination. Averages were also established for the following periods: from 7 days before insemination to the insemination day, from 3 days before insemination to the insemination day and from the insemination day to 3 days postinsemination. Based on the odds ratios, the likelihood of conception rate increased significantly by factors of 1.48, 1.47, 1.5, and 1.1 for the respective maximum THI classes <70, 71-75, 76-80, and 81-85 only on Day 3 before AI, while on the insemination day, it increased by factors of 1.73, 1.53, 1.11, and 1.3 for the respective maximum THI classes <70, 71-75, 76-80, and 81-85. In a subsequent logistic regression excluding mean and maximum THI, the effectiveness of temperature at predicting conception rate was evaluated. Although high, the fit of the second logistic regression model was slightly lower than that of the full model (P=0.88 versus P=0.98, respectively) and the information provided by the THI model. The likelihood of conception rate increased significantly by factors of 1.5, 1.2, 1.0, 1.0 for the respective maximum temperature classes <20, 21-25, 26-30, 31-35 degrees C on Day 1 after AI. The choice of the THI or temperature to monitor the farm environment would have to depend on the particular farm and situation. In our study conditions, the use of maximum temperature alone gives a new point of view regarding the information provided by the THI variables.
夏季热应激是全球温暖地区高产奶牛群受孕率低的一个主要相关因素。我们通过检查10964次授精情况，评估了西班牙东北部高产奶牛受孕率的几个气候变量的影响。将温度湿度指数（THI）与其预测受孕率的效率方面的最高温度进行了比较。记录了每头动物的以下数据：牛群、泌乳次数、授精次数、授精日期、输精公牛和人工授精技术员，以及气候变量，如授精前第7至1天、授精当天以及授精后1、2和3天的各个时间点的平均温度和最高温度、降雨量、平均THI和最高THI。还计算了以下时间段的平均值：从授精前7天到授精当天、从授精前3天到授精当天以及从授精当天到授精后3天。基于优势比，仅在人工授精前第3天，最高THI类别<70、71 - 75、76 - 80和81 - 85的受孕率增加的可能性分别显著提高了1.48、1.47、1.5和1.1倍，而在授精当天，相应最高THI类别<70、71 - 75、76 - 80和81 - 85的受孕率增加的可能性分别提高了1.73、1.53、1.11和1.3倍。在随后排除平均THI和最高THI的逻辑回归中，评估了温度预测受孕率的有效性。虽然第二个逻辑回归模型的拟合度较高，但略低于完整模型（分别为P = 0.88对P = 0.98）以及THI模型提供的信息。在人工授精后第1天，最高温度类别<20、21 - 25、26 - 30、31 - 35摄氏度的受孕率增加的可能性分别显著提高了1.5、1.2、1.0、1.0倍。选择THI还是温度来监测农场环境将取决于特定的农场和情况。在我们的研究条件下，仅使用最高温度就提供了关于THI变量所提供信息的新视角。
