夏季悄然而至，高温高湿的天气又要威胁到牧场的正常管理运营了。奶牛遭受热应激会出现繁殖性能下降、机体免疫力下降、产奶量下降和牛乳品质下降等一系列问题。如何能在热应激期间管理好牧场、饲养好奶牛，这对每一个牧场主来说都是不小的挑战。

Summer is coming quietly, and the high temperature and humidity will threaten the normal management and operation of the ranch again. Dairy cows suffering from heat stress will have a series of problems such as decreased reproductive performance, decreased immunity, decreased milk production and decreased milk quality. How to manage the pasture and raise the cows during heat stress is a challenge for every rancher.

l 不要紧张——热应激是可以预防的

 Don't stress - heat stress is preventable

炎热的夏季会对奶牛造成伤害，找到能减轻奶牛热应激的方法可以防止产奶量的下降，并维持牛群的健康。热中性区是奶牛最喜欢的理想温度范围。在爱荷华州立大学的网络推广研讨会上，农业工程师Brian Dougherty提到，奶牛适宜的最佳温度范围为40℉-70℉（约4℃-21℃）。

Hot summers can take a toll on cows, and finding ways to reduce heat stress in cows can prevent a drop in milk production and maintain the health of the herd. The thermoneutral zone is the ideal temperature range that cows like best. In a webinar at Iowa State University, agricultural engineer Brian Dougherty mentioned that the optimal temperature range for cows is 40°F-70°F (about 4°C-21°C).

l 什么情况下使用自然通风

 When to use natural ventilation

牛舍的通风有很多选择，来自MRCVS的Nigel Cook认为这些通风系统都可以非常有效地运作。与此同时，他认为任何系统也可能因为设计而失败。为了给你的牛舍设计合适的通风系统，“与那些知道自己在做什么的人合作，做出好的选择。” Nigel Cook在Hoard’s Dairyman网络研讨会上说。“如何选择设计通风系统受到很多因素的影响，”他继续说。对于一种特定的情景，通风系统的设计可能取决于气候、牛舍布局、经济效益等因素。牧场员工是否定期清理和维护风扇也需要被考虑在内。

There are many options for ventilation in a cowshed, and Nigel Cook from MRCVS believes that these ventilation systems can all work very efficiently. At the same time, he believes that any system can also fail by design. To design the right ventilation system for your cowshed, "work with people who know what they're doing and make good choices," Nigel Cook said in a Hoard's Dairyman webinar. "How you choose to design a ventilation system is influenced by many factors," he continued. For a particular scenario, the design of the ventilation system may depend on factors such as climate, barn layout, economics, etc. Whether the ranch staff regularly cleans and maintains the fans also needs to be considered.

l 热应激可不止降低产奶量这么简单

 Heat stress can do more than reduce milk production

七月，高温高湿悄然而至，随之而来的就是奶牛热应激。幸运的是，一些应对策略能够帮助牧场主减轻热应激的相关风险并限制其长期影响。在夏季和初秋，许多牧场主都经历过泌乳牛的体细胞数（SCC）升高的情况。在这样的季节中，由于奶牛花费更多的时间在凉爽的地方站立或躺卧，而花费在采食上的时间较少，因此牛群产奶量出现明显下降。热应激会导致应激激素水平升高，从而干扰免疫系统对于致病菌的防御作用。

In July, high temperature and high humidity came quietly, followed by heat stress in dairy cows. Fortunately, several coping strategies can help ranchers mitigate the risks associated with heat stress and limit its longterm effects. During summer and early fall, many ranchers experience elevated somatic cell counts (SCC) in lactating cows. During such seasons, there is a marked drop in milk production in the herd as cows spend more time standing or lying down in cooler areas and less time eating. Heat stress can lead to elevated levels of stress hormones that interfere with the immune system's defenses against pathogenic bacteria.

l 青年围产牛也需要降温

 Young perinatal cow also need to cool down

热应激会降低泌乳期奶牛的采食量和产奶量，这是人所共知的。但是，热应激也会对干奶期的奶牛产生显著影响，您知道吗？干奶期母牛暴露于热应激环境中，其泌乳性能受到损害是因为妊娠后期乳腺的生长受到了影响。在美国，干奶期母牛的热应激给整个行业造成的损失达到了8亿美元，因此越来越多的牧场主对干奶期的母牛也会给予降温措施，以使干奶期的母牛免受热应激的伤害。然而，很少有牧场主对还没有产过犊的青年母牛采用降温措施，这是不对的，青年围产牛也需要降温措施的保护。

Heat stress is known to reduce feed intake and milk production in lactating cows. However, heat stress can also have a significant effect on dry off milk cows, did you know that? In dry-off milk cows exposed to heat stress, lactation performance is impaired because mammary gland growth is affected later in gestation. Heat stress in dry-off milk cows costs the industry $800 million in the U.S., so more and more ranchers are cooling dry off milk cows to keep them are protected from heat stress. However, few ranchers use cooling measures for young perinatal cows that have not yet calved, which is wrong, and young perinatal cows also need protection from cooling measures.

l 为犊牛提供降温措施

 Provide cooling measures for calves

热应激会带来方方面面的挑战。对于犊牛而言，热应激管理也应该引起牧场主的重视。从多个角度来说，年幼的犊牛承受着独特的挑战。犊牛的肺系统功能还不成熟，饮水或干物质采食量有限，从而增加了犊牛降低内部热负荷的困难。对于奶牛而言，喘气是体内主要的热交换机制之一，而对犊牛来说，肺部发育不全，该方式的散热效率低于成年奶牛，喘气会增加体内二氧化碳的排出，减少唾液中的碳酸氢盐，因此患代谢性酸中毒的风险更高。

Heat stress presents challenges in all aspects. For calves, heat stress management should also be a concern for ranchers. Young calves face unique challenges in several ways. The calf has an immature lung system and limited water or dry matter intake, making it more difficult for the calf to reduce its internal heat load. For dairy cows, panting is one of the main heat exchange mechanisms in the body, while for calves, the lungs are underdeveloped, and the heat dissipation efficiency of this method is lower than that of adult cows. Panting will increase the excretion of carbon dioxide from the body and reduce the amount of bicarbonate in saliva, and therefore a higher risk of developing metabolic acidosis.

l 快速识别热应激的早期迹象

 Quickly identify early signs of heat stress

热应激会对动物的生产性能产生严重的负面效应，如产奶量下降、繁殖性能降低、日增重下降等。牛和小型反刍动物遭受热应激后会有如下行为的变化：呼吸短促、呼吸频率增加、大量出汗、躺卧时间减少、反刍活动减少以及采食量下降等现象。

Heat stress can have serious negative effects on animal performance, such as decreased milk production, decreased reproductive performance, and decreased daily gain. Cattle and small ruminants exposed to heat stress have behavioral changes such as shortness of breath, increased respiratory rate, profuse sweating, decreased lying time, decreased ruminant activity, and decreased feed intake.