Thermoregulatory characteristics of dairy cows of different genetic groups in tropical environment summer

Abstract

The thermoregulatory characteristics of three genetic groups of dairy cows (Holstein, Holstein x Gir and Holstein x Jersey) were evaluated in tropical environment, during the summer. Thirty animals were used being 10 in each group. The rectal temperature (RT), respiration rate (RR), sweating rate (RS), maximum environment temperature and air humidity were recorded. The values of environment temperature were above the thermal comfort zone for dairy cows. All values of RT were inside of the normality amplitude, indicating homoeothermic condition. The values of RR were high,showing a constant necessity of thermolisys. The average values of TS on Holstein cows showed high dispersion and also on Holando jersey, but in his group with a lower intensity and the Girolando group expressed less dispersion. The animals maintained a stable body temperature despite of the use of respiratory thermolysis. The definition of differences between individuals related with their sweating ability can support the establishment of selection criteria for animals more suitable for hot environments.