Heat tolerance responses in a Bos Taurus cattle herd raised in a Brazilian climate

The objectives were to verify the morphological and physiological responses related to adaptation to heat of taurine breeds raised under in Brazilian meteorological conditions in different seasons of the year and day periods, and to detect differences within and between breeds to know breed is most adapted. Measurements were made of 74 young bulls (n = 31 Angus; n = 43 Simmental) for the morphological traits: hair length (HL), number of hairs (NH), and coat thickness (CT); and for the physiological traits: respiratory rate (RR) and hair coat surface temperature (ST). The temperature-humidity index (THI) was calculated. The data were subjected to analyses of variance, cluster analysis, and principal component analysis (PCA). The THI (<74) indicates thermal comfort. In the winter, the HL and CT higher than in the spring season (P<0.0001) in both breeds. Angus exhibited higher HL and CT (P<0.0001). Within each breed, the animals differed from one another for HL (P<0.0005). In the spring, CT was similar between the breeds, differing only in the winter season. Angus had higher values (P<0.0005) of RR and lower values (P<0.0001) of ST. Both breeds had higher (P<0.0001) RR and ST in the afternoon. PCA showed that NH and HL better explained variation in adaptation. In general, the breeds have similar morphological responses in the hottest months, but have different physiological responses; Simmental proves to be more physiologically resistant. The afternoo...
Source: Journal of Thermal Biology - Category: Biology Source Type: research