Abstract

The test was conducted, at the facilities of the Dual Purpose Dairy Program of the University of Panama in Chiriqui, Panama, to quantify the main climatic variables during the dry season and their effect on so me physiological indexes of lactating and growing hybrid dairy cattle. The physiological variables were analyzed using the split-plot experimental design in time and contrast of polynomial regression. Ten lactating hybrid cows, with and average weight of 446 kg and a milk production of 6.8 kg/cow/day, and ten calves weighing 118 kg each were used. The animals were Holstein/Brown Swiss X Zebu crossbreeds. The micro-climatic characterization, based on solar radiation, ambient temperature and the temperature-humidity index, indicated that the day time period during the dry season is the representative type of effective climatic heat stress,lactating cows and calves were affected by heat stress, and quadratic and cubic increases were observed in rectal temperature and the respiratory index over the normal physiological pattern.