LAUSR

Abstract In this study we compared the bio-thermal responses of a crossbred (F1, Nellore x Angus) and purebred Bos indicus (Nellore) cattle kept under moderate thermal conditions. Specifically, we assessed if they were different in their daily pattern of metabolic heat production, regulation of body temperature and use of evaporative heat transfer pathways. Six Nellore bulls with 669 ± 65 kg of body weight and twelve crossbred bulls (F1, Nellore x Angus) with 606.5 ± 25.09 kg of body weight, were evaluated in two experiments. Individual bulls were secured and attached to instruments in the biometeorology laboratory to enable recording of the proportion of respiratory gases in the exhaled air (oxygen, O2; carbon dioxide, CO2), saturation pressure of the exhaled air (PS{TEXP}, kPa) and skin surface (PS{TSKIN}, kPa), respiratory rate (RR, breath min−1), ventilation rate (VE, L s−1); skin (TSKIN,°C), hair coat (TS,°C), rectal (TR,°C) and exhaled air temperatures (TEXP,°C) from 0600 to 1800 h. The air temperature over the two experiments ranged from 16 to 30°C. The mean of metabolic heat production was higher for crossbred (2.24 W kg−1) than Nellore cattle (1.09 W kg−1) (P