Berman A
Department of Animal Science, Faculty of Agriculture, Hebrew University, Rehovot Campus, Rehovot, 76100, Israel,
Int J Biometeorol. 2014 Sep;58(7):1683-91. doi: 10.1007/s00484-013-0712-5. Epub 2013 Aug 16.
A model for predicting inter-animal radiant heat exchange in shaded animals is presented, with emphasis on mature cattle. When a cow's surface temperature is 35 °C, as is common in warmer climates, it loses ∼510 Watt m(-2) as radiant heat. Net radiant heat balance depends on radiation coming from bodies in the vicinity. In the 30 °C radiant temperature shaded environment typical of warm climates, net radiant loss from a lactating cow is ∼60 Watt m(-2), i.e., 30 % of its ∼173 Watt m(-2) heat production. Cows rest for 8-14 h day(-1). The heat exchange of a lying cow differs from that of a standing one: the body center is low and 20-30 % of its surface contacts a surface of relatively low heat conductance. Lying reduces the impact of the surrounding shaded area on heat exchange but increases that of heat radiating from neighboring cows. When a cow rests adjacent to other cows, with 1.25 m between body centers when in stalls, it occupies about 140° of the horizontal plane of view. Heat emitted from the animal's surface reduces the net radiant heat loss of a resting cow by ∼30 Watt m(-2). In contrast, the presence of cows at 5 and 10 m distance, e.g., cows resting on straw in loose yard housing, reduces the net radiant heat loss of the resting cow by 9 and 5 Watt m(-2), respectively. Radiant heat input increases with animal density, which is beneficial in cooler climates, but acts as a stressor in warm climates.
本文提出了一种预测阴凉处动物间辐射热交换的模型，重点是成年牛。当奶牛体表温度为35℃时（在温暖气候中很常见），其以辐射热形式散失约510瓦/平方米的热量。净辐射热平衡取决于附近物体发出的辐射。在温暖气候中典型的30℃辐射温度的阴凉环境下，泌乳奶牛的净辐射热损失约为60瓦/平方米，即占其约173瓦/平方米产热的30%。奶牛每天休息8 - 14小时。躺卧奶牛的热交换与站立奶牛不同：身体中心较低，且其20 - 30%的体表与热导率相对较低的表面接触。躺卧减少了周围阴凉区域对热交换的影响，但增加了相邻奶牛辐射热量的影响。当一头奶牛与其他奶牛相邻休息时，在牛栏中身体中心间距为1.25米，它占据了水平视野平面约140°的范围。动物体表散发的热量使休息奶牛的净辐射热损失减少约30瓦/平方米。相比之下，距离5米和10米处有奶牛（例如在散栏牛舍中躺在稻草上休息的奶牛）时，分别使休息奶牛的净辐射热损失减少9瓦/平方米和5瓦/平方米。辐射热输入随动物密度增加，这在较凉爽气候中是有益的，但在温暖气候中则成为一种应激源。
