Mitigating Summer Infertility for Sows

Just like it’s important to keep boars cool for optimum semen quality, follicular development in sows relies on heat abatement, feed intake and boar exposure. ( Alison Fulton )

Written By Randy Bowman and Amanda Minton, The Maschhoffs

The ideal time to breed a sow is within seven days postweaning, with the best fertility achieved at day four and five. Anything longer than seven days increases the risk of missing the breed target or causing the farm to breed lower quality sows. However, it is not uncommon for sows to experience extended wean-to-estrus intervals, poor conception rates, irregular returns and increased embryonic death during the summer. Parity one (P1) sows, in particular, are more sensitive to heat stress and will delay expressing estrus, or standing heat, postweaning. The bottom line is stressed females will deprioritize pregnancy when challenged.

So, how can you ensure you’re keeping the cycle moving?

The Big Three

Fertility is all about follicular development. Without proper management in the summer to account for increased temperatures, sows experience seasonal anestrus, or seasonal infertility, at a larger level. This is especially true in P1 sows that are lactating for the first time. These females are still growing, have less body stores and are more impacted by increased temperatures.

It starts with keeping pigs cool and comfortable, with the goal around getting animals to continue eating and drinking. No pig wants to eat when it’s hot, and breeding animals are no exception. Just like it’s important to keep boars cool for optimum semen quality, follicular development in sows relies on heat abatement, feed intake and boar exposure (see diagram above).

  • Heat abatement: Having plenty of water available and reducing movements in peak temperature periods in the afternoon can help immensely in the summer months. Also, make sure cool cells, fans, inlets and misters are functioning correctly in the barns to reduce heat stress in animals and increase the chances sows will continue eating.
  • Feed intake: Get sows in the proper condition going into farrowing, and then help them maintain condition while they are lactating. Fat sows that come into farrowing are more likely to get hot and not eat. Scoring sows’ body condition every 30 days and calibrating feeder boxes is imperative to ensure each sow is getting the right amount of feed to maintain an ideal body condition. P1 sows that don’t eat well during lactation have a much harder time expressing estrus postwean.
  • Boar exposure: When heat checking, each group of five sows or gilts should get about five minutes of boar exposure daily. Boar exposure should start day one after weaning. It’s important to pay attention to age, temperament and body condition of the boars in use. The active, more aggressive boars with the strongest odor will produce the most pheromones to stimulate follicular growth.


Other measures for reducing seasonal infertility center on handling, both of the animals and of semen. First-parity females are the most prone to wean-to-estrus delays, so pay close attention to them. These sows should be grouped together in the coolest part of the room for breeding and gestation to ensure workers can closely monitor any changes in feed and water intake and body condition, as well as for heat checking and breeding. If grouped together, the job of monitoring this subgroup is simplified for the staff and makes it easier for the manager to observe key animals quickly.

Start heat-checking animals early in the morning, with breeding following as early as possible. Again, moving animals during the cooler parts of the day will help reduce stress. Keep in mind, bred sows should not be moved days three through 35 of gestation, if at all possible.

Another factor to help mitigate risk is proper semen temperature. Semen should be stored between 61°F and 64°F. In general, the optimum temperature is 62°F, and for every 10 minutes semen is at the wrong temperature, motility is reduced by 10%. Make sure you have enough cooler space that tubes are not stacked more than two deep. Avoid stacking multidose semen bags to help maintain the proper temperature.

Only take as much semen as you’re going to use to the barn and place cool packs that are at the same temperature as the semen on the top and bottom of the cooler with doses. When using multidose bags, include gel packs in the backpack. Rotate the multidose bag every five sows to suspend sperm cells and decrease variation in dose concentration.

These are all steps you can start taking immediately to ensure a smooth summer for breeding.  


Randy Bowman is director of technical support at The Maschhoffs. He was raised on a diversified farm in western Illinois and attended Western Illinois University.
Amanda Minton is associate director of reproductive technology at The Maschhoffs.