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Cool, comfortable cows can increase summer pregnancy rates

Mark Carson Published on 09 August 2013

When looking at pregnancy rate data for many dairies, you can instantly tell when summer begins without even looking at the date.

It’s not uncommon to see pregnancy rates cut in half during the hottest periods of the summer. Pregnancy rates commonly slide back as conception and insemination rates are reduced from the summer’s heat.



This makes controlling temperature one of the more critical aspects of managing your cows’ comfort. A lactating dairy cow with more than 55 pounds of dry matter fermenting and breaking down in her rumen usually doesn’t have much of a problem keeping warm.

In fact, depending on the humidity, when temperatures begin to climb above 68ºF your cows will start to become heat-stressed. A temperature of 70ºF with a humidity of 70 percent is enough to cause heat stress in your cows.

What can you do to combat the heat and minimize its impact on your herd’s profitability? How do you minimize that summer drop in pregnancy rate?

To maximize pregnancy rate, you need to first understand why it has decreased. Is the reduction in pregnancy rate due to not catching cows in heat?

Or is the reduction in reproductive performance more driven by the conception rate, with cows simply not conceiving after insemination? It is important to know which factors are driving the drop to help you decide where to focus your resources.


If your herd has a drop in conception rate during the summer months, cooling cows is going to be the prime focus.

When looking at cooling, you want to make sure temperatures are reduced in three areas of the barn: the bunk, the parlor and the stalls. Without cooling, fertility is affected by the physiological and metabolic stress being caused by the rise in temperature.

The first area of focus is the temperature at the stall. Freestall cows spend approximately 14 hours in stalls (both lying and standing), making it the area where they spend the greatest amount of time.

A Wisconsin study following 14 cows housed in a three-row freestall barn found that average lying time was reduced by approximately three hours when periods of heat stress were occurring.

The decreased lying time meant the cows were spending more time standing in the alley and less time in their stalls resting and ruminating. Make sure your cooling strategy includes fans that are focused on moving the air in the area of the stall, since cows spend the majority of their time in this area.

Cooling at the bunk is also another critical spot because of the all-important dry matter intake. Cows spend an approximate average of four hours in the area of the bunks feeding.


In recent years, research has shown the benefit of having sprinklers at the bunk in addition to fans, which help to keep cows comfortable.

A University of Kansas study monitored the performance of dairy cows in 88ºF air temperature at 57 percent humidity, a similar condition that many can face in the middle of the summer.

The Kansas data showed that when cows are soaked with a sprinkler for one minute every five minutes, with fans running continuously, cows were approximately 34ºF cooler in core body temperature than their herdmates with fan cooling only.

The sprinkler-and-fan cows also took nearly half the amount of breaths per minute than fan-only cows. This helps to show that a sprinkler at the bunk significantly helps to lower the effects of heat stress.

Rumination technology is starting to give us insight into heat stress as well. Working with some on-farm automated rumination monitoring equipment, heat-reducing strategies can be seen.

In one dairy last summer, two groups had sprinklers at the bunk while the other two groups had no sprinklers available to them. The rumination data showed the cows in the non-sprinkler group ruminated on average 50 minutes less in comparison to cows that had the extra cooling.

The final area of focus should be the holding area in the milking parlor. With cows being jammed tight in the holding area of parlors, temperature can rise.

Make sure you have fans moving the air through this area of the barn and minimize the amount of time cows spend in the holding area. If you make sure your cows are cool in these three areas of the barn, your conception rate will benefit from less-stressed cows.

The above cooling strategies will help with insemination rates, but it is important you utilize all the tools and strategies available to increase number of pregnancies. Monitor to make sure your target days in milk at first breeding has been met.

During high-temperature periods, timed A.I. should be deployed to help make up for missed heats. It doesn’t hurt to be a little more aggressive with timed A.I., especially if your herd historically sees a drop in heat detection during the summer months.

Also, make sure regularly scheduled pregnancy checks happen during the summer so open cows are identified and re-bred in a timely manner.

Often problems from summer heat stress are compounded less with frequent herd health visits. The longer open cows go unidentified after breeding, the more costly it is for the pocketbook. PD

References omitted due to space but are available upon request. Click here to email an editor.


Mark Carson