Thermal equilibrium and methane emission of Jersey dairy cows
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Meteorological variables have direct influences over physiological, behavioural and performance of animals. The Jersey breed shows a good potential to be managed under tropical environment conditions due to their genetic, adaptive and productive characteristics. To confirm this potential, studies on the thermal equilibrium of these animals must be coupled to methane emission. The aim of the present work was to study the thermal equilibrium of Jersey cows under tropical conditions. Twelve Jersey cows with 326.28 ± 30 kg body weight, 17.66 ± 1.8 milk yield, and 165.5 ± days in milking were assigned in two latin square (LS) designs, fed twice daily under a total mixed ration of corn silage (70%) and grain (30% corn and soybean). Evaluations were performed from 08:00 to 20:00 (LS1) and from 20:00 to 08:00 h (LS2), protected from solar radiation and rain overnight. Meteorological variables (air temperature and relative humidity, short-wave radiation) and body temperatures of the cows (rectal, skin, surface and exhaled air) were recorded. Ventilation rate, respiratory rate, percentage of oxygen carbon dioxide, and methane from the exhaled air were measured by an indirect calorimetry system, using a facial mask. From these data, metabolic heat production, respiratory evaporation, sensible heat loss and methane emission were calculated. Data were analysed by the least squares method. Ambient air temperature and relative humidity ranged from 22 to 31 °C and 27 to 88 %, while short-wave radiation was higher than 600 W m-2 during the hottest hours of the day. The cows presented increase of body temperatures during the hottest hours of the day, correlated to a decrease of sensible heat flow and higher respiratory evaporation. The metabolic heat production was stable and higher than 200 W m-2 during the hottest hours and the methane emission had two apparent rise peaks after feeding times (09:00 and 18:00 h, respectively). From the data obtained, enteric methane emission of confined Jersey dairy cows bred in tropical environment is approximately 184 g per day per cow. These results can be an indicative of the potential of Jersey cows in comparison with other temperate breeds