6 min read
Heat stress in cows happens when they can't dissipate the heat they generate, leading to discomfort and lower milk yields. Unlike humans, cows can start feeling heat stress at temperatures above 20°C. You might notice that your cows breathe faster, graze less, drink more, and move slower in warm weather. Providing shade and ample drinking water is the first line of defence against heat stress. You can also make strategic changes to their management and feeding routine. The podcast included here provides scientific explanations and in-depth strategies for managing heat stress.
Heat stress occurs when cows have more heat than they can get rid of and leads to discomfort and lower milk production. All areas of New Zealand get hot enough to cause heat stress during summer.
We all have an ideal temperature range within which we feel comfortable and our immune system and organs function properly. The comfortable temperature range for a cow is 4-20°C, lower than for a human of 16-24°C.
That’s because cows generate enormous amounts of energy digesting food and producing milk. This is handy during winter but a challenge during summer, when cows absorb more heat from the environment and it’s harder for them to maintain an ideal body temperature.
One way cows get rid of excess heat is by evaporation through their breath and sweat. To increase evaporation, they breathe faster and sweat more, although their ability to sweat is limited. When this isn’t enough, they eat less to reduce the production of heat in their rumen, so their milk yield declines.
High humidity, little cloud cover, and low air movement increase the risk of heat stress as evaporation is less effective, making it hard for the cow to lose heat by sweating and panting.
Watch for these five signs:
The earliest indicator of heat stress is increased breathing rate. Check breathing rate by observing a number of cows on a warm summer afternoon – a high producing black cow will be most at risk. More than 10 breaths in 10 seconds means a cow is not comfortable and is an indication that the herd need cooling.
To minimise impacts on productivity and protect cow comfort, consider the following:
Cows are highly motivated to seek shade during hot weather because shade will keep the cows 2 degrees cooler than direct sunlight.
Sprinklers can improve evaporative cooling for 2-6 hours after wetting.
Note: Sprinklers are not effective unless they thoroughly wet the coat, as this only increases humidity, making heat stress conditions worse.
For technical specifications on sprinkler system design, visit the DairyAustralia website.
Lactating cows typically require more than 100 litres/cow/day in summer and drink between two to six times per day. A cow can drink 20 litres per minute.
Cows walking to milking and standing on unshaded yards during the heat of the day increases risk of heat stress.
Peak heat production in the rumen occurs about three hours after cows eat. The impact of modifying diet is small relative to the impact of providing shade and cooling. However, there are some changes that can help keep your cows cooler:
How does heat stress affect cows, what are some warning signs, and what can you do on farm to make life more comfortable for your cows? In this episode, Tom Buckley, farm manager for Owl Farm in Cambridge, goes into detail about the strategies they use to combat heat stress. Meanwhile, DairyNZ’s Jac McGowan talks about the science behind heat stress: how it affects cows, the warning signs, and what research is underway.