ISSUE FOCUS 34 FEED & ADDITIVE MAGAZINE June 2023 Heat stress has been a major herd management challenge for dairy farmers over many years, presenting severe production and welfare demands in the face of ever-rising global temperatures. Now, with elevated temperature periods becoming increasingly common, and the impact of heat stress forecast to impose an estimated $5 billion a year cost on the dairy sector by 2050 (Wankar et al., 2021), the need for action has never been greater. Implementing top level herd management practices during heat stress has always been important as an essential approach to dairy cow care and will undoubtedly intensify as high temperature and humidity episodes continue to increase. Alongside such techniques, the potential for yeast-based solutions to help reduce the worst impacts of heat stress on farm livestock will almost certainly have a growing part to play in the future of global dairy farming. IMPACT Heat stress triggers an increase in a dairy animal’s core body temperature, lifting it above what is considered normal and shifting it towards potentially dangerous levels. Left to themselves, cows implement their own defence mechanisms. These include panting, standing rather than resting, and cutting back on heat generation activities, such as eating and ruminating. In addition to these responses indicating a downturn in the health of heat stressed livestock, they also signal that production and reproductive functions are being placed under severe pressure. While heat stress fall-out is most pronounced in high performing cows, average milkers and young stock are also at risk when exposed to a high Temperature Humidity Index (THI) of 68 or more. This is the acknowledged threshold at which rising temperature and humidity factors typically trigger negative symptoms. THI 68 equates to a temperature of 22°C and 50% humidity. The higher the THI score becomes, of course, the more damage is caused to affected animals. According to Bernabucci et al. (2010), each THI unit in excess of 68 causes a decline in milk output of 0.27 kg. This is an alarming fact, given that severe heat stress conditions today can easily reach THI 80 or more. FARMER ACTION There are a number of practical steps for farmers to take to help livestock cope with rising THIs. These include providing extra shade, ventilation, cooling, and a plentiful supply of fresh, cool drinking water. Striving to maintain feed intake levels by HEAT STRESS: MEASURES TO COPE WITH RISING TEMPERATURES AND HUMIDITY Erika PAIVA Ruminant Global Program Manager Phileo by Lesaffre
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