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Dairy cows in pasture-based systems are more susceptible to heat stress. Holstein cows have the black or red phenotypes, the latter having lower absorbance of solar radiation. Therefore, the study's objective was to evaluate whether cows with red (R) coats are more resistant than black (B) cows to hot weather in a subtropical climate. R and B lactating Holstein cows were evaluated during the cold and hot seasons for internal and surface temperature and sweating rate. In the cold season, body temperature (n = 9/group) did not differ between groups, but the average superficial temperature (n = 13/group) was lower in R cows (B: 30.9 ± 0.3 °C; RW: 29.6 ± 0.3 °C; p = 0.02). In the hot season, under mild to moderate heat stress, mean body temperature (n = 9/group) of R cows was lower (B: 38.75 ± 0.01 °C; R: 38.62 ± 0.1 °C; p=<0.0001), whereas no difference was observed in superficial temperature (n = 17/group). The maximum internal temperature and sweating rate (n = 11/group), measured in the hot season, and the number of evaluations in hyperthermia in both seasons did not differ. Therefore, there were differences in thermoregulation between phenotypes under mild to moderate heat stress conditions. However, considering that only discrete differences were observed, the red and white coat is unlikely to benefit the Holstein cow's welfare under mild to moderate thermal stress. [Display omitted] • Red and black Holstein cows were evaluated in the hot and cold seasons. • Body temperature of red Holstein was lower in the hot season. • Surface temperature of black Holstein was higher in the cold season. • Sweating rate in the hot season did not differ between red and black Holstein cows. [ABSTRACT FROM AUTHOR]

Heat stress is one of the greatest issues of the dairy industry in regions with hot climate. Since coat color appears to be related to heat stress adaptiveness, we compared rectal temperatures and surface temperatures of Red-and-white (RW, n = 14) and Black-and-white (BW, n = 16) Holstein cows using infrared thermography in both cold (July; mean temperature: 15.5 °C) and hot (March; mean temperature: 30.5 °C) seasons in Southern Brazil. Thermographic images were taken from the left side of the animal at a distance of 4 m. The images obtained were then analyzed using the software Testo IRSoft. The variables obtained by thermography of the body surface include the temperature of non-pigmented patches, obtained using the average of five spots on white patches in a rectangle drawn on the body of the cow from the scapula to the ilium of the cow until the middle of the ribs; the temperature of pigmented patches, obtained using an average of 5 pigmented spots on the same rectangle; the temperature at the hottest spot and the temperature at the coldest spot, within the same rectangle. Rectal temperature measures were taken by a mercury thermometer during milkings. In our findings, during the cold season, RW cows had lower temperatures on the surface of pigmented spots (p = 0.01) but did not differ from BW animals when comparing rectal temperatures (p = 0.70). During the hot season, however, RW cows had lower temperatures on white spots (p = 0.049) as well as lower rectal temperatures (p = 0.029). These results suggest that the red coat phenotype presents less absorption of solar radiation, retaining less heat. • Red-and-white Holstein cows presented lower rectal and surface temperatures than black-and-white cows during the hot season. • Differences in temperatures were less remarkable during the cold season. • Infrared thermography can be a useful tool to identify heat stress in cattle by measuring the surface temperature. [ABSTRACT FROM AUTHOR]