Thermal equilibrium of Nellore cattle in tropical conditions: an investigation of circadian pattern
Cíntia Carol de Melo Costa
Alex Sandro Campos Maia
Marcos Chiquitelli Neto
Vinicius de França Carvalho Fonsêca
, Bruno Rodrigo Simão
Patric André Castro
10.6084/m9.figshare.5176576.v1
https://cbbiomet.figshare.com/articles/journal_contribution/Thermal_equilibrium_of_Nellore_cattle_in_tropical_conditions_an_investigation_of_circadian_pattern/5176576
<p>The aim of this study was to evaluate the circadian
pattern of the thermal equilibrium of Nellore cattle in a tropical environment.
The study was conduct at the Animal Biometeorology Laboratory of the São Paulo
State University, Jaboticabal, Brazil (21.25° S, 601 m altitude) in December of
2016. Six Nellore cattle with similar weight, age and body condition were
assigned in two Latin Square experimental design (24 classes of hours (1-2h;
3-4h; …; 23 - 24h; 24 -1h) during twelve days). Evaluations were performed with
subjects protected from direct solar radiation and rain overnight. Respiratory
parameters as percentage of oxygen (O<sub>2</sub>; %), carbon dioxide (CO<sub>2</sub>;
%), water vapor pressure (e{T<sub>E</sub>}; kPa) respiratory rate (R<sub>R</sub>; breaths min<sup>-1</sup>)
and ventilation (V<sub>E</sub>; L s<sup>-1</sup>) were quantified using an
indirect calorimetry system; furthermore, hair coat surface (T<sub>S</sub>,
°C), skin (T<sub>EP</sub>, °C) and
rectal temperature (T<sub>R</sub>, °C) were recorded with thermocouple. Metabolic
heat production (q<sub>met</sub>), sensible heat flow (q<sub>sens</sub>), heat
loss from respiratory tract (q<sub>er</sub>) and cutaneous evaporation (q<sub>es</sub>)
were calculated. Air temperature (T<sub>A</sub>,°C),
relative humidity (R<sub>H</sub>, %), partial vapor pressure (e{T<sub>A</sub>},
kPa), solar irradiance (G<sub>S</sub>, W m<sup>−2</sup>), black globe
temperature in shade (T<sub>G</sub>,°C),
and under direct sunlight (T<sub>GSUN</sub> ,°C) were measured at regular one-minute intervals
during each day with a portable weather
station. Data were analyzed by the least square method. T<sub>AR</sub> showed, on average, 9°C of amplitude,
with higher value at 13:00 h (30.9 ± 0.2 °C). Average metabolism of 158.43 ±
13.97 W m<sup>-2 </sup>was observed, presenting highest value of 174.62 ± 2.63
W m<sup>-2</sup> at 11:00 h, during the morning; thenceforth, it was gradually
decreasing, and start to increase one hour after feeding time. The sensible
heat flow through the body surface was represented, in highest percentage, by
long wave radiation. Interestingly, even with the fall of the T<sub>AR</sub> at
night, we observed lower values for q<sub>rad</sub>. q<sub>es</sub> was more expressive during the
warmer temperatures. The q<sub>er</sub> seems to be a mechanism of minor
significance for the thermal of Nellore cattle. Under
tropical condition, from 21 to 30 °C thermoregulatory responses of Nellore
cattle remain stable over the 24 hours when protected from direct solar
radiation and rain overnight, which seems to be a good indicative of lower
energetics costs for homoeothermic maintenance.</p>
2017-08-08 15:03:58
beef cattle
indirect calorimetry
thermal balance
Environmental Management