EFFECT OF EVAPORATIVE COOLING PROCEDURE O N THE THERMOREGULATION FUNCTIONS OF HEIFERS RAISED IN DIFFERENT TEMPERATURE AND HUMIDITY CONDITIONS

The aim of this experiment was to verify the effect of evaporative coo ling procedure (ECP) at the temperatures above 25 degrees C on the org anism of heifers reared in three different temperature and humidity co nditions of environment and to determinate how long one minute of ECP has a positive response of the thermoregulation functions of heifers. Three groups of heifers (crossbreds of Czech Pied cattle with Holstein -Friesian) were observed. First group was housed at the temperatures a bove 27 degrees C and had been accustomed to an ECP for the period of one month. Second group was kept under the same temperature conditions with no ECP. Third group was stanchioned at the temperatures around 1 4 degrees C and were transferred to the barn with the temperature abov e 27 degrees C one hour before measurement. Changes of respiration rat e and volume, oxygen consumption, production and flow of heat, pulmona ry ventilation before, during and after ECP were measured in all the h eifers. Heifers exposed and accustomed to ECP for a long time when hou sed at temperatures above 27 degrees C responded positively during and after ECP in all the observed respiratory functions and heat producti on. The ratio of the heat flow by respiration to the total heat flow d ecreased, the heat loss was mostly by passive flow through the mist pa rticles. One minute of sprinkling positively affected thermoregulative functions of an organism for 20-25 minutes. In heifers reared at the high temperatures without ECP the response was positive - to the first sprinkling - in all observed functions just for a short period. Heife rs long-term reared at the air temperatures about 14 degrees C and sud denly transferred to the environment with the temperatures above 27 de grees C reacted to ECP by turning on chemical thermoregulation. The su dden changes of air temperatures and humidity caused heat stress in he ifers, which is percetible from the sudden changes of the observed phy siological functions. It can be claimed that ECP is profitable to perf orm regularly during the whole summer period in a mild zone also in yo ung cattle pf milk or combined breeds because ECP positively stimulate s physiological functions of an organism, which is in relation with th e welfare of animals, health condition and production of animals.