Research Aims to Develop Boars More Tolerant of Gestational Heat Stress

In utero heat stress of boars is a significant threat to pork production, and a University of Nebraska–Lincoln reproductive physiologist is leading a research team that aims to develop boars that are more genetically tolerant of gestational heat stress.

In the United States, about 6 million sows a year produce a litter after exposure to gestational heat stress, a threat that is increasing with climate change. At an average of 11 animals in a litter, that's 66 million piglets affected each year in the U.S. alone.

Researchers have known for decades that direct exposure to summer heat stress dramatically impairs sperm production in adult males. In addition, new evidence demonstrates that exposure to in utero heat stress, or IUHS, also impairs boar sperm production, decreasing counts by about 24% and increasing the proportion of abnormal sperm by about 42%. That renders the semen poor quality, said Amy Desaulniers, assistant professor of veterinary medicine and biomedical sciences and the project's principal investigator.

"The developing male is especially sensitive to gestational insults, which can impair fetal testis development and predispose a lifetime of reproductive failure," Desaulniers said.

Boar fertility is critical for the swine industry, which relies almost exclusively on artificial insemination. A typical boar sires an average of 8,398 progeny per year, compared to 23 progeny per year for a sow.

"Therefore, the boar has the greatest cumulative impact on swine reproductive performance and drives genetic progress in the herd," Desaulniers said.

Scientists don't know the biological mechanisms that underlie IUHS's negative impact on the boar testis, so her research team hopes to determine the physiological effects of IUHS on endocrine function and gamete production within the boar testis. Then, they'll try to develop strategies to make boars more tolerant of in utero heat stress.

"The overall goal is to better understand how IUHS impairs boar reproductive physiology while simultaneously testing a novel IUHS mitigation strategy — genomic selection for heat tolerance," Desaulniers said. "The rationale is that this work will advance our understanding of the biological pathways affected by IUHS in reproductive organs of the boar.

"This research is significant because implementation of this new knowledge is expected to lead to novel methodologies to enhance gonadal function of boars, including gamete production. Ultimately, these outcomes will increase boar fertility, swine reproductive efficiency and the sustainability of U.S. pork production."

Desaulniers said solutions might include pharmacological approaches, new genetic tests or dietary changes.

Improving pork productivity is key to feeding a growing world population and increasing profitability for producers in Nebraska and throughout the United States, Desaulniers said. Pork is the most consumed meat worldwide, and demand is expected to increase 37% by 2050.

The research is funded by a three-year, $650,000 grant from the U.S. Department of Agriculture's National Institute of Food and Agriculture. The research team also includes Brett White, associate professor of animal science; Jay Johnson, USDA-Agricultural Research Service; Clay Lents, U.S. Meat Animal Research Center; and Luiz Brito, Purdue University.