Shade, water, salt and ventilation are key components to minimizing negative effects of heat on beef and dairy cows
By Jackie Clark
Many farmers across Ontario experienced high temperatures and humidity over the last week. Heat stress can affect the health and productivity of both beef and dairy cattle, whether they’re housed in a barn or in the pasture. Producers can take steps to mitigate the negative effects of heat stress on their herd.
“Cattle have an ideal temperature range, so they prefer temperatures between 5 and 22 C (41 and 72 F),” James Byrne, beef cattle specialist at the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), told Farms.com.
Mario Mongeon, livestock specialist at OMAFRA, agreed.
“Heat stress for the dairy cow is happening at a much lower temperature than one would expect,” he said. The degree of stress depends on both temperature and relative humidity. 22 C (72 F) and 50 per cent relative humidity “would be enough to trigger some sort of reaction from dairy cows, because they’re cool-loving animals.”
Producing dairy cows suffer from heat stress at a lower temperature “because lactating cows are producing milk (and) they have a higher core temperature naturally because of milk production,” Byrne added.
As humidity increases, all cattle will experience heat stress at a lower temperature, he explained. For animals housed inside, ventilation to control humidity is particularly important as temperatures rise.
For both beef and dairy cattle “the main impact of heat stress is that it reduces their feed intake,” he said. “That means that they’re going to reduce their average daily gain if they’re growing animals.”
Less dry matter intake will also affect milk production.
“When cows eat less, they produce less,” Mongeon said. “Not only will they produce less but it will change what they produce. We will notice modifications in terms of components in the milk.”
Ratio of butterfat and protein in the milk will change, he explained. Dairy “cows with greater production levels will be more affected.”
Similarly, in beef cattle, the largest animals will feel the greatest impact.
“Market-ready cattle are the ones that are particularly at risk,” Byrne said.
“Dark-coloured beef cattle on a high-energy diet carrying a lot of body condition, and animals very close to being market ready” are very dense relative to their surface area, he explained. They generate a lot of heat and have a harder time cooling down.
Young cattle “as a rule of thumb, are better able to cope with heat stress than older animals are,” Byrne added.
However, there can be carry-over effects of heat stress for dairy cows.
Producers tend to focus on their lactating cows, but “young stock as well as dry cows … will also be affected. Differently, but still, the effect can be carried over into the following lactation because of changes that happen during pregnancy,” Mongeon explained.
Farmers may also see “a reduction in breeding efficiency, simply because the animals’ desire to be moving around isn’t particularly there,” Byrne said.
So, what can farmers do to help their hot cows?
“In a nutshell, it’s no different than how (humans) react during a warm spell. We look for shade, we look for water, we look for air movement,” Mongeon said.
“The two basic things that you have to do, is you have to try to provide those animals with shade and water,” he said. “For pasture animals, the best form of shade is some kind of tree cover.” Buildings or tarps also cast shade, however, trees provide an extra cooling effect by evapotranspiration and better structure for ventilation.
Air movement in barns is critical for cooling down animals that are inside, Mongeon said. “In many places now, they have automatic systems that will trigger a sprinkling or misting system.”
Farmers should try to manage cattle so they don’t need to move much in the hottest parts of the day, or several hours afterward.
Cows’ “core temperature peaks about two hours after the peak air temperature, and then they take about six hours to get rid of it,” Byrne explained.
Farmers should supply water close to a shade source “because we don’t want these animals to have to do a lot of work” to hydrate, said Byrne.
Research has shown that increasing ambient temperature from 21 to 32 C (70 to 90 F) can increase water requirements for cattle by 2.5 times, he explained.
A mineral salt block should also be available, because hot animals will “lose a lot of mineral salt” in sweat and urine, he added.
Though it’s not a common practice, some dairy producers who integrate pasture into their system will bring the cows out at night to take advantage of cooler temperatures, Mongeon said.
Digestion generates heat so, if it’s possible to alter feeding, early in the morning or in the evening and nighttime is best, Byrne agreed.
Avoiding heat stress is good for both the cattle and farmers.
Research in the U.S. showed that if producers can reduce body temperature by 1 C (1.8 F), average daily gains can be increased by 1.25 pounds per day, Byrne said. “Keeping those animals cool is important to keep the animal performance progressing.”
OMAFRA has a heat stress in livestock and poultry app that allows producers to calculate the amount of heat stress and recommended actions for seven types of livestock at a given temperature, humidity and ventilation type.
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