Taking preventive steps now can go a long way to ensuring that sow and boar performance survives the steamy months ahead.

“I think the big issue is being ready for it, and managing your operation to reduce its effects,” says Todd See, North Carolina State University (NCSU) swine extension specialist.

Improved Production

The single best measure of financial loss caused by seasonal infertility is measured in the fewer pigs available for sale, says See.

North Carolina producers typically report a 5% reduction in farrowing rates caused by heat stress. “Our studies this past year show that when producers kept the animals cool and comfortable and reduced the heat stress, they saw improvements of 5 to 8% in farrowing rates and litter size compared to summertime breedings from the previous year,” he continues.

Adjusting improvements in performance for a 30% lower heat index this past year, compared to the previous year in North Carolina, See calculates that lessening the seasonal decrease in productivity has saved the state's pork producers a whopping $942,592.

The following list of tips to help producers deal with seasonal infertility was developed by See, NCSU swine specialist Billy Flowers and former NCSU reproductive specialist Kevin Rozeboom. More detailed information on the program can be accessed on their Web site, www.mark.asci.ncsu.edu in the Pig Pen section under reproduction.


Minimum total confinement summer ventilation rates for sow and litter, gestating sow and breeding sow or boar are 500, 180 and 300 cfms/head, respectively. These rates may be doubled in the southern U.S. in summer.

Inspect ventilation systems carefully. Even new systems need occasional adjustments to operate as designed. Fresh air must enter the building at speeds of 600-1,000 ft./min. in order to circulate well and prevent cold air drafts from falling on animals. Fresh air inlets require seasonal adjustments.

Provide and maintain supplemental cooling systems to all totally enclosed sow and boar production units. Cool cells do a good job of cooling the air inside a facility, says See. But when the heat index (combination of temperature and humidity) nears the danger level (see Figure 1), a supplemental cooling system for the animal should be activated. See prefers a dripper or sprinkling system that cools the animal's skin by direct application and evaporation. Pigs are more sensitive to the heat index than humans because they do not sweat.

Evaporative cooling systems and circulatory fans should be considered for naturally ventilated gestation and breeding facilities.

Production Scheduling

Producers typically bring in extra gilts for breeding to combat production shortfalls caused by seasonal infertility, observes See. “But remember, if you bring in extra gilts and you don't allow extra space, you may end up crowding gilts and causing more heat stress.”

Heat stress can also lower sperm production and semen quality in boars. If that happens, they may have reduced fertility for six weeks. That's more serious than if a sow gets heat stressed and doesn't cycle, he points out.

Feed, Water Systems

Maintaining sow feed intake in summer is the most critical management step to reducing the impact of heat stress on seasonal infertility, according to the NCSU animal scientists.

Most producers who switch from feeding twice a day to three times a day experience a 10 to 15% boost in sow feed intake. Just remember, when you increase feeding frequency, decrease the amount fed each time.

The NCSU specialists say the reason this strategy works is due to the normal increase in body temperature that occurs after a sow eats a meal. The concept is — if a sow consumes smaller meals, her body temperature will not increase as much because there is less feed to digest.

Keep feed fresh. Some reports indicate liquid diets can boost sow feed intake as much as 15%. A drawback is that wet feed quickly becomes moldy. The same is true of adding large amounts of fat to the ration. If done, add small amounts of fat to the diet and check regularly for spoilage. Sows will not eat spoiled feed.

Drinkers need to be checked for adequate flow rates. An increase in temperature from 60° F to 85° F or more will cause pigs to drink 50% more water, notes See. Check troughs to ensure fresh water is being supplied.

Embryo Mortality

Most of this loss occurs in the first two to three weeks postbreeding. To avoid increased embryo mortality, the NCSU team advises:

  • Avoid breedings in late estrus;

  • Reduce stress by mixing females only at weaning. Never mix or move females during the first 35 days after breeding;

  • Refrain from moving females in gestation to different locations; and

  • Avoid changing feeding levels within the first 30 days after breeding. Provide a level plane of nutrition during and after breeding.