Laboratoire de Recherche : Matériaux Molécules et Applications, Institut National Agronomique de Tunisie, Université de Carthage, Tunis, Tunisie.
LR13AGR02: Laboratoire ADIPARA, Higher School of Agriculture of Mateur, University of Carthage, Mateur, Tunisie.
Reprod Domest Anim. 2020 Sep;55(9):1250-1257. doi: 10.1111/rda.13772. Epub 2020 Aug 2.
This work aims to study the relationship between variations of the Temperature-Humidity Index (THI) and the parameters of reproduction especially the first conception rate (FCR) and to determine the threshold THI value where cows' fertility rate dropped in 12 Holstein dairy herds raised in the arid climatic conditions of Tunisia. THI values were calculated over 22 years (1996-2018), and the mean monthly temperature and relative humidity data were obtained from the Meteorological Institute of Tunisia. A total of 20,396 individual records (Insemination and calving dates) were extracted from the Livestock and Pasturing Office (OEP, Tunisia) with regard to the highest THI before breeding, on the breeding day, and after breeding. Statistical analysis was performed using the GLM procedure of SAS software. Results point to the fact that a summer heat stress exists in southeast Tunisia and lasts for 4 months starting from June until September with THI values fluctuating between 73 ± 2.38 and 79 ± 3.01 exceeding, therefore, THI threshold of 72. Increased THI from ≤70 to ≥80 units was associated with drops in conception rate (CR) and fertility rate (FR) of 49% and 45% giving a correlation with the THI of (r = -.72, p < .05) and (r = -.74, p < .05), respectively. When cows were inseminated on extremely hot days (THI ≥ 80) preceded by cooler temperatures, pregnancy by service (P/AI) was 7% points higher than for other cows that were exposed to high temperatures before breeding. The average number of insemination was higher (p < .05) from THI ≤ 70 (2.01) compared to THI ≥ 80 (3.41). Cows calving during an absence of heat stress (THI ≤ 70) have the shortest average calving intervals (CI: 420 ± 15.1 days). Contrastly, calving in the condition of heat stress (THI ≥ 80) has the longest CI (487 ± 12.8 days). For each point increase in the THI value above 67, there is a decrease in the first conception rate by 1.39%. In this particular arid environment, high-yielding Holstein cows' breeding success is strongly affected by heat stress that takes place just before or after breeding.
本研究旨在探讨温度-湿度指数（THI）的变化与繁殖参数之间的关系，特别是首次受孕率（FCR），并确定在突尼斯干旱气候条件下饲养的 12 个荷斯坦奶牛场中，奶牛繁殖率下降的 THI 阈值。THI 值在 22 年间（1996-2018 年）进行了计算，月平均温度和相对湿度数据是从突尼斯气象研究所获得的。从牲畜和牧场办公室（OEP，突尼斯）提取了 20396 个个体记录（授精和分娩日期），这些记录与配种前、配种当天和配种后的最高 THI 有关。统计分析采用 SAS 软件的 GLM 程序进行。结果表明，突尼斯东南部存在夏季热应激，从 6 月持续到 9 月，持续 4 个月，THI 值在 73±2.38 到 79±3.01 之间波动，超过了 72 的 THI 阈值。THI 从≤70 增加到≥80 单位与受孕率（CR）和繁殖率（FR）下降 49%和 45%相关，与 THI 的相关性分别为（r=-0.72，p<.05）和（r=-0.74，p<.05）。当牛在极其炎热的天气（THI≥80）进行授精，且之前的温度较低时，与其他在授精前暴露在高温下的牛相比，妊娠率（P/AI）高出 7%。当 THI≤70 时，授精的平均次数更高（p<.05）（2.01），而当 THI≥80 时（3.41）。在没有热应激（THI≤70）的情况下分娩的奶牛具有最短的平均产犊间隔（CI：420±15.1 天）。相反，在热应激（THI≥80）条件下分娩的奶牛具有最长的 CI（487±12.8 天）。THI 值每增加 1 分，首次受孕率就会下降 1.39%。在这种特殊的干旱环境下，高产荷斯坦奶牛的繁殖成功率受到配种前后发生的热应激的强烈影响。
