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Abstract：
High temperature is an environmental factor that impairs sow fertility. In this study, we identified the critical weeks for heat stress effects on aspects of fertility performance, namely weaning-to-first-service interval (WSI) and farrowing rate (FR). We also examined the threshold temperatures above which the fertility performance deteriorated and whether there were any differences between parities regarding heat stress effects or thresholds. Performance data of sows in 142 herds from 2011 to 2016 were matched to appropriate weekly averaged daily maximum temperatures (Tmax) from weather stations close to the herds. Two types of ratios (i.e., ratio for WSI and odds ratio for FR) were used to identify the critical weeks for heat stress by comparing the respective measures for two sow groups based on Tmax in different weeks around weaning or service events. The ratios for WSI were calculated between groups of sows exposed to Tmax ≥ 27 °C or <27 °C in each week before weaning, with the Tmax cutoff value based on a recent review study. Similarly, the odds ratios for FR for the two groups were calculated in weeks around service. The weeks with the largest differences in the fertility measures between the two Tmax groups (i.e., the highest ratio for WSI and the lowest odds ratio for FR) were considered to be the critical weeks for heat stress. Also, piecewise models with different breakpoints were constructed to identify the threshold Tmax in the critical week. The breakpoint in the best-fit model was considered to be the threshold Tmax. The highest ratios for WSI were obtained at 1 to 3 wk before weaning in parity 1 and 2 or higher sow groups. The threshold Tmax leading to prolonged WSI was 17 °C for parity 1 sows and 25 °C for parity 2 or higher sows. Increasing Tmax by 10 °C above these thresholds increased WSI by 0.65, and 0.33 to 0.35 d, respectively (P < 0.01). For FR, the lowest odds ratios were obtained at 2 to 3 wk before service in parity 0, 1, and 2 or higher sow groups. The threshold Tmax leading to reductions in FR was 20, 21, and 24 to 25 °C for parity 0, 1, and 2 or higher sow groups, respectively. Increasing Tmax by 10 °C above these thresholds decreased FR by 3.0%, 4.3%, and 1.9% to 2.8%, respectively (P < 0.01). These results indicate that the critical weeks for heat stress were 2 to 3 wk before service for FR and 1 to 3 wk before weaning for WSI. The decreases in fertility performance in parity 0 to 1 sows started at temperatures 3 to 8 °C lower than in parity 2 or higher sows.
摘要：
高温是影响母猪繁殖力的环境因素。在这项研究中,我们确定了热应激对生育能力影响的关键周，即断奶至首次服务间隔(WSI)和分娩率(FR)。我们还检查了阈值温度，高于该阈值温度时，生育能力会下降，以及在热应激效应或阈值方面，奇偶校验之间是否存在任何差异。从2011年到2016年，142只母猪的性能数据与接近牛群的气象站的每周平均每日最高温度（Tmax）进行了匹配。两种类型的比率(即，WSI的比率和FR的比值比）用于确定热应激的关键周，方法是根据断奶或服务事件前后不同周的Tmax比较两个母猪组的各自指标。在断奶前每周暴露于Tmax≥27°C或<27°C的母猪组之间计算WSI的比率，Tmax临界值基于最近的一项综述研究。同样，两组的FR比值比是以服药周为单位计算的.两个Tmax组之间生育率指标差异最大的周(即，WSI的最高比率和FR的最低比值比)被认为是热应激的关键周.此外，构建具有不同断点的分段模型以确定关键周的阈值Tmax。最佳拟合模型中的断点被认为是阈值Tmax。在第1和2或更高的母猪组中，断奶前1至3周获得了最高的WSI比率。导致WSI延长的阈值Tmax对于奇偶校验1母猪为17°C，对于奇偶校验2或更高的母猪为25°C。Tmax在这些阈值以上增加10°C，WSI增加0.65，0.33至0.35d，分别为(P<0.01)。对于FR，最低的比值比在第0,1和2或更高的母猪组服役前2到3周获得。对于奇偶校验0、1和2或更高的母猪组，导致FR降低的阈值Tmax为20、21和24至25°C，分别。将Tmax增加10°C，高于这些阈值，将FR降低3.0%，4.3%,和1.9%至2.8%，分别为(P<0.01)。这些结果表明，热应激的关键周为FR服务前2至3周，WSI断奶前1至3周。产次0至1头母猪的育性表现下降始于3至8°C的温度，比产次2头或更高的母猪低。
