Effect of rising ambient temperature and humidity beyond thermoneutral zone on production performance of exotic and Sahiwal cattle in NWFP, Pakistan

The effect of ambient temperature (maximum) and percent moisture in air on average Total Monthly Milk Yield (TMY) of HF cows, Jerseys and Sahiwals was ascertained using regression analysis. A curvilinear relationship existed between average TMY and month of Production in the three pure breeds. The three slopes for HF cows, Sahiwals and Jerseys indicated significant (P less than 0.01) association between average TMY and month of production. In general, smaller average TMY in all purebred cows was found in summer than in winter. The minima in production were hit when temperature was maximum and relative moisture in air was lower. The effect of increasing humidity was not clearly indicated. Productivity of cows in the three pure breeds was adversely affected by rise in ambient temperature above the upper limit (24 degree centigrade) of the zone of thermoneutrility. The average temperature in colder months in NWFP (December through March) ranged from 1.74 to 24.37 degrees centigrade, which could be considered the most favorable range for the three pure breeds. In other wards, the average maximum temperature of 24 degree centigrade could therefore, be considered the upper limit of comfort zone for the three pure breeds in the context of the present study. An increase of 21.23 degree centigrade in ambient temperature from January through June caused a simultaneous decrease of 93.86 liters of TMY. For each month separately, the magnitude of decrease in TMY was however, variable. Results did not indicate a linear reduction of TMY with increasing maximum ambient temperature. Each degree successive rise in temperature accompanied smaller and smaller reduction in milk secretion. The cows some way resisted the adverse effect of ever increasing temperature at lower production level. Thus at the maximum summer temperature the milk secretion minimally dropped than the amount recorded at the previous (Lower) level of ambient temperature. These observations suggested that at lower level of production the deleterious effects of high temperature were smaller than at higher level of production. In other words, the production of high yielding cows would be more severely affected than low yielding cows in a warm environment. Breeds in warm environment would have attained adaptation at the expense of reduced productivity.