奶牛热应激指数的研究现状及问题分析

热应激严重影响奶牛的生产力、繁殖力和福利。为降低奶牛热应激的风险,国内外学者一直在寻求预测和评估热应激的方法,在诸多方法中综合多个环境因子的热应激指数模型目前最为常用。为避免在指数选择上的盲目性,该文系统地梳理了温湿指数、基于温湿指数的修正指数和其他指数,对比分析了不同评价指数在奶牛热应激时表征指标的差异,其中涉及指数阈值、环境因子及传热性质、奶牛生理反应与指数间的关系。目前奶牛热应激指数存在的问题有指数包含的环境参数不能反映奶牛与环境的换热机理,以及环境条件不同导致评价结果差异较大等。随着数字化技术的应用,多参数获取技术得到了根本性改变,有必要提出更加精细的指数评价模型以满足提高家畜生产力、实现福利化养殖的需要。作者对未来奶牛热应激指数发展方向上的建议是:1)应涉及更多的环境参数,并且环境参数应体现出一定的换热机理;2)构建特定气候类型指数的同时,还应适当考虑指数在其他环境下的适应性;3)指数要有适用信息和阈值,指数的阈值要能够进行动态调整以扩大其适用范围;4)指数的构建应综合考虑动物因素和环境因素,可考虑与动物热平衡原理相结合。

Research status and existing problems in establishing cow heat stress indices

Heat stress seriously affects the productivity, fertility and welfare of dairy cows. It is to be expected that, in the course of the next few decades, climate conditions for raising cattle will deteriorate. In order to reduce the risks of heat stress in dairy cows, researchers have been trying to seek a reliable method to predict or evaluate heat stress, and it has been become to a hot topic in this research field to obtain an index model by combining multiple environmental factors. To avoid blindness in selecting these environmental factors, this paper systematically analyzed the temperature-humidity index, and its modified indices based on THI combined with other factors, and compared the differences among these indices in characterizing the heat stress of dairy cows. These differences relate to the thresholds of indices, environmental factors involved and heat exchanging properties, and the relationships between physiological responses of dairy cows and indices. In this paper, the problems of heat stress index of dairy cows are also discussed. The most widely used temperature-humidity index is based on thermal sensation and thermal comfort of human, but had not been actually related to cow''s living environments. Most indices linking environmental parameters to the physiological or behavioral responses of cows were established through the statistical correlation analysis process, but it did not reflect the real physical significance of the effects of environmental parameters on the process of heat exchange between animals and its environmental factors. In addition, the indices could only be well applied to the situation where they were established properly with the sufficient information for their use. We believed that THI had played an important role in the past when environmental parameters, physiology indicators and behavior responses were hard to be obtained, but the problem of THI had been existing in its application, so other direct parameters such as heat tolerance of high-yielding cows, the change of building structure and the linkage of various cooling modes should be considered when a new THI is being designed. Otherwise, the current THI will be not to meet the future production requirements of the dairy farming industry. With the application of digital technology, multi-parameter acquisition technology has been fundamentally changed, so it is necessary to develop a more reliable index of evaluating heat stress for cows to meet the needs of increasing livestock productivity and achieving welfare. Our suggestions to achieve this goal are as follows: 1) The index should be developed to incorporate more environmental parameters reflecting heat transfer mechanism. 2) The index can be applied not only in some specific climatic conditions, but also in other climatic conditions. 3) The index is to have applicable conditions and thresholds, and the thresholds of the index should be able to be dynamically adjusted to extend the scope of its application. 4) The index should be linked to animal physiological parameters and environmental factors, and consideration could be given to constructing a new index by meeting the theory of animal thermal balance.