Changes in frequency and severity of heat waves due to climate change pose a considerable challenge to livestock production systems. Although it is well known that heat stress reduces feed intake in cattle, effects of heat stress vary between animal genotypes and climatic conditions and are context specific. To derive a generic global prediction that accounts for the effects of heat stress across genotypes, management and environments, we conducted a systematic literature review and a meta-analysis to assess the relationship between dry matter intake (DMI) and the temperature-humidity index (THI), two reliable variables for the measurement of feed intake and heat stress in cattle, respectively. We analysed this relationship accounting for covariation in countries, breeds, lactation stage and parity, as well as the efficacy of various physical cooling interventions. Our findings show a significant negative correlation (r = − 0.82) between THI and DMI, with DMI reduced by 0.45 kg/day for every unit increase in THI. Although differences in the DMI-THI relationship between lactating and non-lactating cows were not significant, effects of THI on DMI varied between lactation stages. Physical cooling interventions (e.g. provision of animal shade or shelter) significantly alleviated heat stress and became increasingly important after THI 68, suggesting that this THI value could be viewed as a threshold for which cooling should be provided. Passive cooling (shading) was more effective at alleviating heat stress compared with active cooling interventions (sprinklers). Our results provide a high-level global equation for THI-DMI across studies, allowing next-users to predict effects of heat stress across environments and animal genotypes.

气候变化导致的热浪频率和严重程度的变化对畜牧生产系统构成了相当大的挑战。虽然众所周知，热应激会降低牛的采食量，但热应激的影响因动物基因型和气候条件而异，并且因环境而异。为了得出一个通用的全球预测来解释热应激对基因型、管理和环境的影响，我们进行了系统的文献回顾和荟萃分析，以评估干物质摄入量 ( DMI ) 和温湿度指数之间的关系。 THI)，两个可靠的变量分别用于测量牛的采食量和热应激。我们分析了这种关系，解释了国家、品种、哺乳期和胎次的协变，以及各种物理降温干预措施的功效。我们的研究结果显示THI和DMI之间存在显着的负相关 ( r  = − 0.82) ，每增加一个THI单位，DMI就会减少 0.45 公斤/天。尽管泌乳和非泌乳奶牛的DMI - THI关系差异不显着，但THI对DMI的影响不同的泌乳阶段。物理降温干预（例如提供动物遮荫或庇护所）显着缓解了热应激，并在THI 68 之后变得越来越重要，这表明该THI值可以被视为应提供降温的阈值。与主动冷却干预措施（洒水器）相比，被动冷却（遮阳）在缓解热应激方面更有效。我们的结果为跨研究的THI-DMI提供了一个高级全局方程，允许下一个用户预测热应激对环境和动物基因型的影响。