Mainly in hot climate conditions, the beef cattle production under pasture can be improved with the use of natural shade to minimize the heat stress. Therefore, the objective of the present study was to evaluate the effect of the thermal stress using thermal comfort indexes on the beef cattle production under different conditions of natural shade. This study was carried out in the West region of the State of Paraná in January and February 2007. The experimental design was completely randomized with three treatments constituted of trees forming small forests, isolated trees and not shaded condition. Each one of these treatments was submitted a group of ten animals of the Nelore breed (replications). The daily values of wind speed, black globe, dry bulb temperature and wet bulb temperature were registered every each three hour, from 9 a.m. to 6 p.m. The temperature of the animal body surface was also registered with the same frequency. For each treatment, based in these measured, the temperature and humidity index (THI), black globe and humidity index (BGHI) and the radiant heat load (RHL) were calculated. The THI values varied from 70 to 87, from 73 to 93 for the BGHI and from 450 to 672 W m-2 for the RHL. The environment that provided the best thermal conditions for the animals was constituted by small forests of Guajuvira trees.
beef cattle; bioclimatology; thermal comfort
