Department of Animal Sciences, University of Florida, Gainesville 32611-0910.
Agriculture Victoria Research, AgriBio, Centre for AgriBioscience, Bundoora, Victoria 3083, Australia; School of Applied Systems Biology, La Trobe University, Bundoora, Victoria 3083, Australia.
J Dairy Sci. 2022 Sep;105(9):7820-7828. doi: 10.3168/jds.2021-21741. Epub 2022 Jul 22.
Heat stress has negative consequences for milk production and reproduction of dairy cattle. These adverse effects are likely to increase because of climate change and anticipated increases in milk yield. Some of the variation among cows in ability to resist effects of heat stress is genetic. The current objective of this observational study was to assess the effectiveness of the Australian breeding value for heat tolerance (ABVHT) based on the decline in milk yield with heat stress for predicting cow differences in effects of heat stress on regulation of body temperature, milk production, and reproductive function. Genomic breeding values for heat tolerance were calculated for 12,487 cows from a single California dairy farm. Rectal temperature in the afternoon (1100-2045 h) was measured on a subset of 626 lactating cows with ABVHT ≥102 (heat tolerant) or <102 (heat sensitive). Rectal temperature was 0.12°C lower for heat-tolerant cows than heat-sensitive cows. Vaginal temperatures were measured every 15 min for 5 d in 118 cows with ABVHT ≥108 (extreme heat tolerant) or <97 (extreme heat sensitive). Vaginal temperature was 0.07°C lower for extreme heat-tolerant cows than extreme heat-sensitive cows. Lactation records for 4,703 cows with ABVHT were used to evaluate seasonal variation in first 90-d milk yield, fat percent, and protein percent for each ABVHT quartile. Overall, cows with higher ABVHT had lower milk yield, fat percentage, and protein percentage and higher first service pregnancy rate. There was no summer depression in production or reproduction or interactions between season and ABVHT quartile. We observed that ABVHT can successfully identify heat-tolerant cows that maintain lower body temperatures during heat stress. The lack of a pronounced seasonality in milk production or reproduction precluded evaluation of whether ABVHT is related to the magnitude of effect of heat stress on those traits.
热应激对奶牛的产奶量和繁殖性能有负面影响。由于气候变化和预期的产奶量增加，这些不利影响可能会增加。奶牛对热应激影响的抵抗力的一些差异是遗传的。本观察研究的目的是评估基于产奶量随热应激下降的耐热性澳大利亚选育值（ABVHT）预测奶牛对体温调节、产奶量和繁殖功能的热应激影响差异的有效性。从加利福尼亚州的一个单一奶牛场的 12487 头奶牛中计算了耐热性的基因组选育值。在具有 ABVHT≥102（耐热）或<102（敏感）的 626 头泌乳牛中，测量了下午（1100-2045h）的直肠温度。耐热牛的直肠温度比敏感牛低 0.12°C。在具有 ABVHT≥108（极端耐热）或<97（极端敏感）的 118 头奶牛中，每 15 分钟测量一次阴道温度，持续 5 天。极端耐热牛的阴道温度比极端敏感牛低 0.07°C。使用具有 ABVHT 的 4703 头奶牛的泌乳记录，评估了每个 ABVHT 四分位数的首次 90 天产奶量、脂肪百分比和蛋白质百分比的季节性变化。总体而言，ABVHT 较高的奶牛产奶量、脂肪百分比和蛋白质百分比较低，首次配种妊娠率较高。产奶量或繁殖力没有夏季下降，也没有季节和 ABVHT 四分位数之间的相互作用。我们观察到，ABVHT 可以成功识别在热应激期间保持较低体温的耐热牛。产奶量或繁殖力没有明显的季节性，因此无法评估 ABVHT 是否与热应激对这些性状的影响程度有关。
