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The dynamic adaptation of Brazilian Brahman bulls.

Authors :: Façanha DAE
Ferreira JB
Morais Leite JHG
de Sousa JER
Guilhermino MM
Costa WP
Bermejo Asensio LA
de Vasconcelos AM
Silveira RMF
Source :: Journal of thermal biology [J Therm Biol] 2019 Apr; Vol. 81, pp. 128-136. Date of Electronic Publication: 2019 Feb 25.
Publication Year :: 2019
Abstract: Heat stress is one of the most important factors that affect the performance of some Bos taurus breeds and crosses in tropical regions. The Brahman breed was developed in hot regions of the world and often has genes that confer resistance to heat stress compared to other breeds of beef cattle. The goal of this work was to evaluate the adaptive responses of Brahman bulls, based on physiological, hormonal and hair characteristics according to season. The physiological, hormonal and hair characteristics were rectal temperature (R <subscript>T</subscript> ), respiratory rate (R <subscript>R</subscript> ), sweating rate (S <subscript>R</subscript> ), triiodothyronine (T <subscript>3</subscript> ), thyroxine (T <subscript>4</subscript> ), cortisol concentrations (C <subscript>O</subscript> ), coat thickness (C <subscript>T</subscript> ), hair length (H <subscript>L</subscript> ), hair diameter (H <subscript>D</subscript> ) and hair density (N <subscript>D</subscript> ). These were recorded in Brahman bulls from a Cerrado biome during four seasons: spring (21 September to 20 December), summer (21 December to 17 March), autumn (18 March to 20 June) and winter (21 June to 20 September). Data was analyzed using a general linear model that included season as a fixed effect; in addition, multivariate tests and logistic regression were also used to characterize the animals within each season. The meteorological variables defined the four seasons, besides identifying climatic differences between them. Significant differences (P > 0.05) were found for most of the physiological, hormonal and hair characteristics according to season. The Brahman bulls presented particular adaptive characteristics in each season. Individually, most of the Brahman bulls presented the same adaptive reaction in each season; particular similarity occurred for the summer and autumn. This pattern is a reflection of the inter-relationships between physiological responses and hair characteristics.<br /> (Copyright © 2019. Published by Elsevier Ltd.)