MORPHO-PHYSIOLOGICAL RESPONSES OF Bos indicus, Bos taurus AND CROSSBRED WEANED HEIFERS TO SEASONAL VARIATIONS.

Beef cattle kept in extensive systems are constantly exposed to the effects of the climate. In tropical and intertropical regions, the reproductive management of Bos taurus animals with B. indicus animals is an alternative for zootechnical improvement. The objective was to evaluate morphophysiological characteristics of heat adaptation of beef heifers on pasture. For this, fifty-four animals from four distinct genetic groups: (1) Nellore, (2) Senepol, (3) Angus x Nellore and (4) ¼ Brahman x ¼ Nellore x ½ Senepol (Tri-cross), with six months-old, were evaluated during the summer and autumn seasons of 2016. The morphological characteristics of the coat (length, diameter, thickness, density and number of hairs and coat color) and physiological (skin, hair and rectal temperature; sweat rate; respiratory and heart rate) were evaluated. The environment was evaluated using the temperature and humidity index, black globe temperature, humidity index and radiation thermal load. We observed that the production environment presented thermal discomfort for the animals. Thus, the animals' rectal temperature differed between seasons. All groups studied showed some adaptive characteristic to the tropical environment. Angus x Nellore heifers had the highest values for the morphological measures in the months evaluated, coinciding with thermal comfort indexes above those considered comfortable for cattle and the lowest value of respiratory rate when compared between the crossing. In conclusion, all genetic groups have at least three adaptive characteristics to the tropical environment when analyzing the physiological responses. [ABSTRACT FROM AUTHOR]