Pages: 18-29

Abstract

In hot climate, the heat stress means that the environmental effective temperature is higher than the animal’s thermo neutral zone. The effective temperature is affected by air temperature, relative humidity, air movement and solar radiation. The degree of heat stress to which the cattle are exposed is estimated using the temperature humidity index (THI). The production and reproduction of the dairy cattle are adversely affected by the heat stress. The adverse effects are: the hypothalamic- hypophyseal-ovarian axis fails to exhibit the oestrus (particularly in the buffaloes), the cows reduce their feed intake, the concentrations of the metabolic hormones are decreased, and the acid- base status of these cows is altered. Subsequently, the fertility of the buffaloes and the milk production of the cows would be decreased. The various strategies could be used to improve the production and reproduction in the heat-stressed cattle. As feeding strategy, the cattle should be fed through the high density diets (high concentrate and low fibre or, supplemented with fat) having low level of crude protein or low degradability in the rumen. Also, the diets of the heat- stressed cows should be supplemented by the buffers in the positive formula of the dietary cation-anion difference (DCAD) expressed as (Na+ K- Cl) m Eq. g-1 dry matter. The DCAD has been suggested to improve the acid-base status. Moreover, the heat-stressed cattle should be shared with fans and sprayers as a management strategy. Actually, the feeding strategy must be paralleled with the management strategy for the heat-stressed cows.