AvaliaÃÃo de estresse tÃrmico em vacas leiteiras mestiÃas (bos taurus x bos indicus) criadas em clima tropical quente Ãmido no estado do cearà / Evaluation of heat stress in crossbred dairy cows (bos taurus x bos indicus) created in hot humid tropical climate in the state of cearÃ

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

11/02/2008

RESUMO

A study was conducted to evaluate heat stress tolerance susceptibility in adult crossbred dairy cows (Bos taurus x Bos indicus), raised in tropical humid climate, at the county of Pacatuba, Ceara state. The study was carried out in 2006. We determined air temperature and air humidity to calc ulate the temperature humidity index (THI) and rectal temperature (RT) of all animals were taken monthly in the morning and afternoon to estimate the index of heat tolerance (IHT), according to the methods of Iberia, Baccari Jr. and Rauschenbach-Yerojhin. Number of animals varied from 14 to 20 per month. Correlations among all variables were determined following Pearsonâs method (p <0.05). Results show that, during the year, animals were subjected to different climates although out of their comfort zone, especially when maximum values of temperature, humidity and THI were measured. Moreover, environment variables showed inverse daily and annual changes. Higher values of humidity were detected in the first semester and in the morning, while higher air temperatures were measured in the second semester and afternoon. THI was more associated with air temperature (r = 0.84) than with humidity (r = - 0.53). Values of RT were better correlated with AT (r = 0.44) then with AH (r = - 0.50) and THI (r = 0.31). Also, there was a transition phase corresponding to the change from rainy to dry seasons, which was associated with an increase in RT and, consequently, decrease in ITH. Among all ITH estimated in the present study, the Iberia index was found to show the highest correlations (r= -0.99; p<0.05) with values of rectal temperature. In conclusion, animals were, along the year, subjected to an environment regarded as out of their comfort zone, especially because of maximum air temperature, air humidity and ITH. Evaluations of ITH and THI could be used as an efficient tool for identification of heat stress tolerance of dairy cows raised in tropical regions

ASSUNTO(S)

zootecnia estresse tÃrmico ambiente Ãndice de tolerÃncia ao calor Ãndice de temperatura e umidade heat stress environment index of heat tolerance temperature humidity index

ACESSO AO ARTIGO

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