Abstract：
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.
摘要：
牧场系统中的奶牛更容易受到热应激的影响。荷斯坦奶牛有黑色或红色的表型，后者对太阳辐射的吸收率较低。因此,这项研究的目的是评估在亚热带气候下，红色（R）皮毛的母牛是否比黑色（B）母牛更能抵抗炎热的天气。在寒冷和炎热的季节评估了R和B泌乳荷斯坦奶牛的内部和表面温度以及出汗率。在寒冷的季节，体温（n=9/组）在组间没有差异，但是R母牛的平均表面温度（n=13/组）较低（B：30.9±0.3°C；RW：29.6±0.3°C；p=0.02）。在炎热的季节，在轻度至中度热应激下，R母牛的平均体温（n=9/组）较低（B：38.75±0.01°C；R：38.62±0.1°C；p=<0.0001），而在表面温度上没有观察到差异（n=17/组）。最大内部温度和出汗率（n=11/组），在炎热的季节测量，在两个季节的高热评估数量没有差异。因此,在轻度至中度热应激条件下，表型之间的体温调节存在差异。然而,考虑到只观察到离散的差异，在轻度到中度的热应激下，红色和白色的外套不太可能有利于荷斯坦奶牛的福利。
