Measuring antibody response to a commonly used vaccination against porcine reproductive and respiratory syndrome virus, or PRRSV, could better predict swine reproductive success than common genetic selection strategies, according to new research conducted at Iowa State University.

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.

“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, assistant professor of animal science at Iowa State, lead researcher on the study.

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.

They showed that antibody response to PRRSV vaccination is highly heritable (34 percent). Also, they showed that antibody response to PRRSV vaccination had high favourable genetic correlation with the number of piglets born alive or stillborn, and pre-weaning mortality. The genetic correlations were not as strong for all the traits studied, although all were in a favourable direction. Thus, they 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. “But immune-related traits are usually not expressed in the nucleus,” said Leticia Sanglard, an Iowa State doctoral candidate in Serão’s lab involved in the study. “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 said. “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 Department of Animal Science at Iowa State were Serão and Sanglard, Professor Rohan L. Fernando and Distinguished Professor Jack C. M. Dekkers. Other partners on the study were Kent A. Gray with Smithfield Premium Genetics; Daniel C. L. Linhares, in the Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State; and Megan C. Niederwerder, in the Department of Diagnostic Medicine/Pathobiology, Kansas State University.

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

Yet waiting for PRRS outbreaks to occur so the trait can be measured limits its use for purposes of routine genetic selection. So the researchers were pleased to see that the relationship between antibody response to PRRSV and reproductive performance also held true for non-infected commercial pigs after exposure to the vaccine.

“These are promising results. 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,” he said. “A number of companies have indicated interest to see how they could use this information to breed more productive, resilient pigs.”