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Heat stress impacts cattle reproduction

by Wyoming Livestock Roundup

Julie Walker, South Dakota State University Extension beef specialist, says working cattle in hot weather can be detrimental when doing heat synchronization and artificial insemination (AI) programs.  

Any time producers have to work cattle, it pays to watch weather forecasts and try to choose a day that won’t be during a heat wave, she says, adding that breeders need to get cattle in for the various steps in a heat synchronization and AI program. Walker adds that timing is crucial, regardless of the weather.  

“More people are going to April and May calving to match forage with nutritional needs of the lactating cow – not having to worry about cold weather in February-March, but now they have to deal with the heat instead,” Walker explains. “Producers are breeding cows in July and August, which are often the hottest months.”

Reproductive practices

As a result, if producers are putting in CIDRs and synchronizing, then having to pull CIDRs, they are under the clock and may have to get those cows in when it’s very hot, Walker says.  

“If they are going to do a fixed-timed AI in the morning, they are probably going to be pulling CIDRs at 7 p.m. the evening before,” she adds. “If the cattle are not very close to the corrals and we have to pull CIDRs at 7 a.m., which might mean we have to go get the cattle at 4 or 5 p.m., that’s still during the hottest part of the day.”

As a result, Walker notes the cows likely won’t be able to rest or cool down because calves need to be sorted off, equating to three or more hours of working cattle in the heat of the day.   

“Producers need to think about the heat and plan ahead. It might be a situation where they want to move the cattle closer to the corrals in the morning, while it’s still cool, so they don’t have to drive them as far to bring them into the facility that evening,” she comments. “Cattle are refreshed and watered before we start working them, reducing the amount of time we have to work them in hot weather.” 

Water availability

“When moving and working cattle this time of year, make sure there is always ample clean fresh water for them, so they won’t have any hesitation about drinking and getting rehydrated,” Walker says.

“If there’s a fountain-type tank, make sure there’s enough water pressure to keep it full.  If there are calves with those cows, we have to make sure the calves can reach the water, if it’s in a tank,” says Walker.

Reproductive impact

Heat stress can also impact reproduction, particularly during early pregnancy for cows.

“Heat also has a negative impact on bull fertility,” says Walker.  

Producers who are utilizing heat detection during hot weather are likely to find that cows aren’t very active during the heat of the day. 

“During the heat of the day, cows will be lying around in the shade if possible and trying to stay cool,” she says, noting producers will have their best luck checking cows for evidence of cycling activity in early mornings or late evening hours, since cows may be most active during the night. “When breeding cows in the summer when it’s hot, it really helps with the heat detection to use patches on the cows, to know which ones have been ridden.”

Walker emphasized, “We may not be out in our pastures during the coolest part of the day and night to see the riding activity, so we can use that tool to help us identify the cows that need to be inseminated.”

Heather Smith Thomas is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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