|CAROL DE MELO COSTA, CINTIA - Sao Paulo State University (UNESP)|
|SANDRO CAMPOS MAIA, ALEX - Sao Paulo State University (UNESP)|
|Brown Brandl, Tami|
|CHIQUITELLI NETO, MARCOS - Sao Paulo State University (UNESP)|
|DE FRANCA CARVALHO F, ONSECA VINICIUS - Sao Paulo State University (UNESP)|
Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2018
Publication Date: 5/1/2018
Citation: Carol De Melo Costa, C., Sandro Campos Maia, A., Brown-Brandl, T.M., Chiquitelli Neto, M., De Franca Carvalho F, O. 2018. Thermal equilibrium of Nellore cattle in tropical conditions: an investigation of circadian pattern. Journal of Thermal Biology. 74:317-324. https://doi.org/10.1016/j.jtherbio.2018.04.014.
Interpretive Summary: Heat stress in beef cattle has both economic and animal well-being implications. High temperature has a greater impact on bos taurus breeds than on bos indicus breeds of cattle. A study was conducted to gain a better understanding on the diurnal patterns of thermoregulation of Nellore bulls. Both meteorological and physiological variables were measured. It was determined in the temperature range from 21.5 ± 0.06 to 30.86 ± 0.07 °C, the respiratory system contributes to thermal regulation of Nellore bulls. However, when air temperature was above 29 °C, heat loss by sweating was the principal way to maintain the thermal equilibrium of adult Nellore bulls. Overall these results indicate Nellore cattle have lower energy expenditure for body thermal regulation (as measured using indirect calorimetry methods), high heat tolerance, and adaptation to tropical environments.
Technical Abstract: The aim of this work was to evaluate the diurnal patterns of physiological responses and the thermal regulation of adult Nellore bulls. Six 30-mo-old Nellore bulls (669 ± 65 kg BW) were randomly assigned to four 6-h periods in a Latin Square design such that measurements of each animal cover a 24-h cycle. Meteorological variables (air temperature, relative humidity, local solar irradiance, ultraviolet radiation, wind speed and black globe temperature) were recorded at regular one-minute intervals with an automated weather station. Respiratory rate, ventilation rate, oxygen, carbon dioxide, methane, saturation pressure, air temperature of the exhaled air, saturation pressure in the air leaving the ventilated capsule placed over the animal surface, hair coat, skin surface and rectal temperature were assessed. The thermal equilibrium was determined according to the principles of the first law of thermodynamics using biophysical equations. Animals were evaluated in an area which was protected from solar radiation, rain, and had a range of ambient air temperature between 20.57 ± 0.07 and 30.86 ± 0.07 °C. Percentage of O2 and CO2 in the exhaled air changed moderately (P < 0.0001) throughout the 24 h, which resulted in an average metabolic heat production of 151.45 ± 13.60Wm-2. At the largest thermal gradient (TS - TA; from 24:00–07:00 h), heat transferred by long wave radiation and surface convection corresponded to near 60% of the metabolism. At 11:00 h the ambient temperature approached 29 °C and latent heat became the main way to cool the body. From this time until 17:00 h, cutaneous evaporation represented approximately 53% of total heat loss. In conclusion, results of the present study seem to be a good indicator of lower energy expenditure for body thermal regulation, high heat tolerance and adaptation of Nellore cattle to the tropical environment.