Shephard R W, Maloney S K
School of Electrical and Data Engineering, Faculty of Engineering & IT, University of Technology Sydney, Sydney, New South Wales, Australia.
School of Human Sciences, Faculty of Science, The University of Western Australia, Crawley, Western Australia, Australia.
Aust Vet J. 2023 Nov;101(11):417-429. doi: 10.1111/avj.13275. Epub 2023 Aug 24.
Cattle control body temperature in a narrow range over varying climatic conditions. Endogenous body heat is generated by metabolism, digestion and activity. Radiation is the primary external source of heat transfer into the body of cattle. Cattle homeothermy uses behavioural and physiological controls to manage radiation, convection, conduction, and evaporative exchange of heat between the body and the environment, noting that evaporative mechanisms almost exclusively transfer body heat to the environment. Cattle control radiation by shade seeking (hot) and shelter (cold) and by huddling or standing further apart, noting there are intrinsic breed and age differences in radiative transfer potential. The temperature gradient between the skin and the external environment and wind speed (convection) determines heat transfer by these means. Cattle control these mechanisms by managing blood flow to the periphery (physiology), by shelter-seeking and standing/lying activity in the short term (behaviourally) and by modifying their coats and adjusting their metabolic rates in the longer term (acclimatisation). Evaporative heat loss in cattle is primarily from sweating, with some respiratory contribution, and is the primary mechanism for dissipating excess heat when environmental temperatures exceed skin temperature (~36°C). Cattle tend to be better adapted to cooler rather than hotter external conditions, with Bos indicus breeds more adapted to hotter conditions than Bos taurus. Management can minimise the risk of thermal stress by ensuring appropriate breeds of suitably acclimatised cattle, at appropriate stocking densities, fed appropriate diets (and water), and with access to suitable shelter and ventilation are better suited to their expected farm environment.
牛在不同气候条件下将体温控制在狭窄范围内。内源性体热由新陈代谢、消化和活动产生。辐射是热量传入牛体的主要外部来源。牛的体温调节利用行为和生理控制来管理身体与环境之间的辐射、对流、传导和蒸发热交换，需注意蒸发机制几乎完全将体热传递到环境中。牛通过寻找阴凉处（炎热时）和遮蔽处（寒冷时）以及挤在一起或站得更远来控制辐射，需注意在辐射传递潜力方面存在品种和年龄的固有差异。皮肤与外部环境之间的温度梯度和风速（对流）决定了通过这些方式的热传递。牛通过控制流向周边的血液流动（生理方式）、短期内通过寻找遮蔽处和站立/躺卧活动（行为方式）以及长期改变被毛和调整代谢率（适应过程）来控制这些机制。牛的蒸发散热主要通过出汗，还有一些通过呼吸散热，当环境温度超过皮肤温度（约36°C）时，这是消散多余热量的主要机制。牛往往更适应较凉爽而非较炎热的外部条件，瘤牛品种比普通牛更能适应炎热条件。通过确保使用适应良好的合适品种牛、保持适当的饲养密度、提供合适的饮食（和水）以及让牛能够获得合适的遮蔽处和通风，管理措施可以将热应激风险降至最低，使其更适合预期的养殖环境。
