AMES, Iowa – Antibody response to a commonly used vaccination against porcine reproductive and respiratory syndrome virus (PRRSV) could better predict swine reproductive success, according to new research conducted at Iowa State University (ISU).

“Based on our findings, swine genetic companies should use antibody response data collected at the commercial level as an indicator trait to indirectly genetically improve reproductive performance in commercial crossbred and purebred sows,” said Nick Serão, ISU assistant professor of animal science, and lead researcher on the study.

The research received support from the Iowa Pork Producers Assoc., and the ISU Graduate College.

According to the ISU College of Veterinary Medicine, PRRSV is a viral disease characterized by two overlapping clinical presentations, reproductive impairment or failure in breeding animals, and respiratory disease in pigs of any age. PRRSV is the most economically significant disease to affect U.S. swine production since the eradication of classical swine fever (CSF).

Researchers said reproductive performance is an important component of success for the swine industry – and genetic selection in purebred herds is the primary strategy the industry uses to improve litter size.

However, reproductive traits are strongly influenced by the environment, while genetics explain only about 10 percent of reproductive outcomes, creating challenges for rapid genetic improvements influencing litter size and survival, researchers said.

Reproductive impairment or failure, more obvious in sows or gilts, also affects some boars. The respiratory syndrome is seen more often in young growing pigs, but also occurs in finishing pigs and breeding stock.

Although reported initially in only a few countries in the late 1980s, PRRSV now occurs worldwide in most major swine-raising countries. PRRSV is prevalent in the United States, and exists both in epidemic and endemic forms.

Serão’s team investigated the relationship between the antibody response to PRRSV vaccination, and several litter size traits in commercial crossbred sows. 

To do this, they vaccinated the non-PRRSV-infected gilts with a commercial modified live PRRSV vaccine. Blood samples were collected about 52 days after vaccination to measure antibody response to PRRSV, and animals were followed for three litters, the study said.

The study said they showed antibody response to PRRSV vaccination is highly heritable (34 percent). Also, they showed antibody response to PRRSV vaccination had high favorable genetic correlation with the number of piglets born alive or stillborn, and pre-weaning mortality. 

Moreover, the genetic correlations were not as strong for all the traits studied, although all were in a favorable direction, the study said. 

As a result, researchers found antibody response to PRRSV is a good candidate to be used as an indicator to genetically improve these traits.

“This trait could be easily measured in commercial gilts, at reasonably low cost,” Serao said. “Fertility traits such as farrowing rate and age at first service could also be improved using this strategy.”

In swine breeding, genetic selection is performed using purebred animals in “nucleus” herds, said Leticia Sanglard, an ISU doctoral candidate in Serão’s lab participating in the study.

“But immune-related traits are usually not expressed in the nucleus,” she said. “One reason for this is high biosecurity in these herds: Only after animals are introduced to commercial farms are they exposed to pathogens and other stressors that challenge their immune systems and trigger expression of such traits.

“Animals that perform better in the nucleus environment do not necessarily perform the best in commercial herds,” she added. “An indicator trait of reproductive performance collected at the commercial level that is highly heritable, such as antibody response to PRRSV, could help obtain faster genetic progress for sows’ reproductive performance.”

Findings from the research were recently published in the peer-reviewed journal, “Frontiers in Genetics.” Co-authors in the ISU Department of Animal Science were Serão and Sanglard, Professor Rohan L. Fernando, and Distinguished Professor Jack C. M. Dekkers. 

Other partners on the study were Kent Gray with Smithfield Premium Genetics; Daniel Linhares, in the ISU Department of Veterinary Diagnostic and Production Animal Medicine; and Megan Niederwerder in the Kansas State University Department of Diagnostic Medicine and Pathobiology.

This new study builds on previous research by Serão and others, which found antibody response to a PRRSV outbreak was a potential trait that could predict reproductive performance. 

Those findings showed increased antibody response to the PRRSV infection was significantly correlated with more piglets born alive – and importantly, that antibody response to the PRRSV infection is highly heritable.  

Serão said waiting for PRRSV outbreaks to occur so the trait can be measured limits its use for purposes of routine genetic selection.

“These are promising results,” he said. “In this area of work, we are always trying to find a novel trait that can be used to improve performance at the commercial level. A number of companies have indicated interest to see how they could use this information to breed more productive, resilient pigs.”

One of those companies is Smithfield Premium Genetics, which also helped support the research.

“We are very interested in developing cutting-edge technology to identify, and select for pigs with better resistance to common diseases such as PRRSV,” said Yijian Huang, a Smithfield geneticist.

“This project allows us to have a better understanding of current commercial females, and their antibody responses,” she said. “With the maturing of the technology, we believe it could be a potential tool to help the industry select animals before PRRSV actually hits a farm.”