Minimizing heat stress impact on breeding stock's performance

Cheryl Day, Former Editor

August 31, 2015

3 Min Read
Minimizing heat stress impact on breeding stock's performance

The hot days of summer can have significant impact on the productivity and health of all pigs as elevated temperatures often reduce the fertility of gilts, sows and boars. Research has shown that females have a prolonged return to estrus or fails to return to estrus after weaning, reducing conception rates.

Judging by the increased sow-herd culling rate from August through December, hog producers in the United States are dealing with loss of productivity (see figure to the right). In order to minimize loss of productivity and profits during the hot summer, the National Pork Board offers these tips.

  • Feed sows when it is cool – Provide feed to sows during the coolest parts of the day. Pigs in the growing and finishing stage will alter their eating behavior by eating more feed in the nighttime hours. Feeding sows in gestation in the early morning can help them stay cooler because the heat associated with digesting and metabolizing their meal dissipates prior to the heat of the day.

  • Check for estrus when it is cool – Check for estrus behavior and breed in the early morning or late evening. Sows are more likely to show estrus signs when it’s cooler, so more animals will be identified in standing heat during the coolest part of the day.

  • Keep boars cool, too – Sows are only half of the reproductive equation, so if you have boars, keep them cool with evaporative coolers or water misters. Boar libido is enhanced when it is cooler, so collect boars early in the morning or in the evening. If using natural service, also take advantage of the coolest part of the day.

Jason Ross, Iowa State University associated professor, in the last heat stress webinar presented by the NPB, recommends selecting breeding stock with production tolerant to heat stress as another tool for reducing costs that are associated with productivity loss during the summer months. Ross explains that “Seasonal infertility represents one of the most costly environmental detriments to swine production efficiency.”  

In a limited study, Ross and a team of researchers are studying the effects of heat stress on breeding stock reproductive performance. The research shows that thermoregulatory response to heat stress in gilts prior to puberty is repeatable in the future. 

He adds that endocrine markers may have usefulness in assessing the biological mechanisms that contribute to infertility in the summer. Identification of genomic regions associated with these responses to heat stress is critical in identifying animals with a production tolerance to heat stress.

Ross and the team of researchers will be continuing its research “Understanding the Biology of Seasonal Infertility to Develop Mitigation Strategies for Swine” in order to uncover more information to assist hog farmers in limiting heat stress impacts.

Ross’s presentation was the last of four webinars hosted by the National Pork Checkoff every Tuesday in August. The Checkoff’s animal science committee selected heat stress for this year's webinar series because it affects all producers regardless of farm size or location, yet producers have few tools to combat the effects of summer heat.

Recordings of the webinar are available at

About the Author(s)

Cheryl Day

Former Editor, National Hog Farmer

Cheryl Day is a former editor of National Hog Farmer.

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