When Mother Nature turns up the heat on your sow herd, reproductive performance can dip drastically. In some cases, seasonal infertility can cut your farrowing rates by as much as 20 percent, hampering your pig flow and your profits.

In addition, litter size can drop by a pig embryo or more, and heat stress can lead to deaths in the first 30 days of gestation. Heat stress during the last 14 days of gestation can increase the stillborn rate as well, says Don Levis, Ohio State University swine specialist.

Seasonal infertility has been a challenge for pork producers forever, and despite technological changes, it shows no signs of tempering. Many thought the industry’s move indoors to confinement units would eliminate or reduce seasonal infertility, but that has not been the case.

“The industry still has a hog cycle, and it’s largely because seasonal infertility problems still exist,” says Duane Reese, swine specialist, University of Nebraska.

Problems with infertility usually start around June and run through August or September, depending on the weather.

“Seasonal infertility looks to be more temperature related than related to day length or amount of light,” says Levis. “The reason is because temperature is more variable from year to year, and seasonal infertility is not a problem for the same producers each year.”

Wayne Singleton, Purdue University swine specialist, agrees that temperature is the most significant factor, but says that the amount of light per day and pigs’ natural instinct to breed in the winter also play a role.

As far as geographic differences, Levis says that even cool states like Minnesota have problems with infertility.

“You can’t draw a geographic line to indicate problem areas, because some animals only need the temperature to exceed 82°F for them to start feeling heat stress,” says Levis. “Most areas in the United States will get above 82°F at some time.”

All hogs, regardless of body composition, genetic line or other traits appear to be, more or less, equally susceptible to seasonal infertility.

Not surprisingly, keeping the sows cool is a major factor in reducing seasonal infertility. Reese suggests you use drip cooling, evaporative pads or snout cooling to help cool sows. He stresses that you must watch all three systems carefully to make sure they are functioning properly.

“I don’t think an evaporative cooler is enough, you need to put water on the hogs as well,” says Levis. “I’m not sure the cool air gets down to the sow level in all of those buildings.”

In his experience, Levis says tunnel ventilation helped but didn’t solve the problem. Evaporative coolers are a good system, provided you supplement it with some kind of sprayer – not mister – to keep the hogs cool, he adds.

On a sow-by-sow basis, Reese recommends watching sow respiration rates. Make sure they are taking 35 breaths per minute or less. If they’re taking more breaths than that, they’re heat stressed.

Another option to keep pig flow in line is to overbreed sows during the summer months. “Look at your records over the last two to three years and adjust your breedings

accordingly,” says Singleton. “You may need to increase your breedings by 20 percent to 30 percent.”

Pay special attention to breeding details during the summer months to further reduce seasonal infertility. If you have boars on the farm, don’t forget to keep them cool. Even well-managed boar studs will probably double the amount of ejaculates they must discard during the summer months due to low semen quality, says Singleton. Also, consider increasing the number of sperm per dose during the hot months of the year.

Make sure you use good quality semen, and don’t stress the sows or move them during periods of high temperatures. In addition, the time of day that you heat check and breed sows takes on more importance during the summer.

While some seasonal infertility is inevitable, there are steps you can take to minimize the impact on your sow herd.

“A lot of problems start in the farrowing house,” says Levis. “If it’s too hot there, sows won’t eat well. Then they leave the farrowing house too thin and often won’t recycle.”

Make sure your sows are getting an adequate supply of high-quality feed during lactation, so their feed intake remains sufficient. Singleton says feeding sows several times a day can help improve feed intake for lactating sows.

Without question, as the temperature starts to rise, you need to be more aware of  and work to minimize the impact of seasonal infertility. In the months ahead, make sure your staff is paying special attention to gestation diets, ventilation, cooling systems and animal handling to keep your farrowing rates and litter sizes as high as they can be, in spite of summer’s heat.