Physiological and thermographic response to heat stress in zebu cattle

Abstract

The objective of this study was to evaluate the heat tolerance of five zebu breeds using physical, physiological and hematological traits as well as thermographic responses. Forty cows of the Gir, Girolando, Nelore, Sindhi and Indubrasil breeds (eight cows each), approximately three years of age, were evaluated. Body weight, withers and hump heights as well as thoracic circumference were recorded. The density and length of the hair was obtained by collecting one square centimeter in the rump region and skin color using the CIELAB system. Rectal temperature, heart and respiratory rates were evaluated during the morning at 4:30h, and in the afternoon, at 14:30h, with six repetitions. Blood samples were collected for hematological evaluation. The surface temperature was obtained using an infrared camera FLIR® T400. Two images were taken from each animal, one laterally of the whole body and the other of the head region. Air temperature, wind speed, relative humidity were obtained from a mobile weather station. The statistics analysis included an analyzes of variance, principal factors, as well as cluster, discriminant and canonical analyzes, logistic regression and calculation of odds ratio. There were significant differences in the rectal temperature, heart and respiratory rates between breeds. Gir and Indubrasil breeds had the highest rectal temperatures. Breed was significant for surface temperatures and showed that physical and physiological factors affected breeds in different ways. Eye and brain surface temperatures were the most affected by environmental parameters. Also, environmental parameters affected packed cell volume and red cell number. Odds ratio test showed that the Gir breed was three times more likely to have higher rectal temperature compared with Sindhi as confirmed by the logistic regression. When the black globe temperature approached 35°C, the probability of the Gir animals having rectal temperatures above normal was approximately 70%. Gir was the breed least adapted to climate conditions of the experiment while the Sindhi and Girolando breeds showed the best physiological response to thermal stress.