Heat Stress in Dairy Animals - Its Impact and Remedies: A Review

One of the greatest challenges to production dairy farmers in most part of the tropical country is heat stress and the strain that it causes the lactating dairy cow. Climatic conditions in the most parts of India are such that the warm (or hot) season is relatively long, there is intense radiant energy for an extended period of time and there is generally presence of high relative humidity. Thus heat stress is chronic in nature; there is often little relief from heat during evening hours, and intense bursts of heat and humidity further depress the performance. Thermal stress has a direct effect on feed intake of the cow, which in turn reduces her milk yield. Body weight losses associated with thermal stress may impair her reproductive performance as well. Moreover, the microclimate modifications may also be of significant consequence in regulating the feed intake of the animals as well as in ensuring high efficiency of nutrients conversion which may otherwise be diverted towards maintenance of body temperature. In heat stressed animal, heat tolerance can be attained either by reduction of his normal heat load (i.e., reduced metabolic rate) or by increased heat dissipation to the environment. Improved heat tolerance coupled with high productivity is thus most likely to be attained by increased heat dissipation. The effects of heat stress are costly to the dairy farmers, but there are opportunities to recover some of the losses to hot weather.