A year ago, sow mortality and pelvic organ prolapse (POP), defined here as vaginal or uterine prolapse, was generally viewed by the global pork industry as a U.S.-specific issue, says Jenelle Dunkelberger, a geneticist with Topigs Norsvin. But recently, she’s received reports of increasing sow mortality in other geographic locations, including Brazil, a major competitor in the global pork market and similar to the U.S. in terms of production practices, in many ways.
“I think sow mortality, especially sow mortality due to POP, is even more relevant than it was a year ago because it’s no longer an issue isolated to the U.S.,” Dunkelberger says. “The call to develop solutions is urgent.”
That’s why a new genomics study is turning heads.
Can Genetics Help Reduce the Incidence of Sow Pelvic Organ Prolapse?
Led by Jack Dekkers, distinguished professor of animal breeding and genetics at Iowa State University, and Vishesh Bhatia, a Ph.D. student in genetics and genomics housed in the Department of Animal Science at Iowa State University, the study used data collected on a total of 14,186 genotyped purebred sows in two multiplier farms across the U.S. from 2012 to 2022. The overall incidence of sow pelvic organ prolapse (POP) among dead and culled sows was 7.1%. For this study, the incidence of POP was defined as the occurrence of vaginal or uterine prolapse, since it was hard to distinguish between the two on-these farms.
“All sows were genotyped for 48,075 genetic markers across the genome. Statistical analyses were conducted to estimate heritability of susceptibility to POP, both across parities and within parities, as well as genetic correlations of susceptibility to POP to determine whether the genetic basis of POP changes with age,” Bhatia says. “In addition, a so-called genome-wide association study (GWAS) was conducted to identify genomic regions that are associated with susceptibility to POP, followed by functional genomic analyses of these regions to identify potential genes and biological processes that are associated with susceptibility to POP.”
Based on this genomic study, the heritability for POP was estimated at 35%, compared to 22% for the original study, which was conducted using pedigree data. The reason for this difference is because using information from genetic markers can more accurately estimate relationships among animals, thus providing more accurate estimates of heritability, the researchers explain. These heritabilities are on the so-called ‘underlying scale of POP risk.’ On the observed scale, i.e. whether the sow actually had POP or not, these translate into heritabilities of 12 and 7%, respectively.
“Susceptibility to POP was confirmed to have a substantial genetic basis in this population and in these herds. This indicates that it can be selected against to increase the longevity of sows,” Bhatia says.
It was also confirmed that susceptibility to POP has a similar genetic basis in different parities. Genome wide association studies revealed six regions across the genome that were associated with susceptibility to POP. However, together, these six regions explained only 9% of the genetic differences between sows.
“This means there are many other genomic regions that contain genes associated with susceptibility to POP but that have small effects. Functional analyses provided further insights into several biological processes that are associated with susceptibility to POP, including the role of collagen, the estrogen receptor gene, and glycoproteins that are important for calcium/phosphorus homeostasis,” Bhatia says.
What Does This Mean for Producers?
Although the researchers admit there is no silver bullet to prevent POP, susceptibility can be reduced by genetic selection because it has a substantial heritability, at least in some populations and herds.
“Using POP data from such herds, breeding companies can select to reduce susceptibility to POP in their lines, using similar procedures as they use to select for, e.g., litter size. In addition, with additional research, the knowledge of the biological pathways that were discovered to affect susceptibility to POP can be used to develop targeted management recommendations or interventions to reduce the incidence of POP in herds across the globe,” Dekkers says.
For Dunkelberger, it was a validation of the work her team started as a result of the Phase I study.
“We implemented direct selection against uterine prolapse in January of 2021,” she says. “This realization, that heritability is 35%, rather than 22%, doesn’t change our approach. But, it validates that we’re on the right track in providing a genetic solution and provides even more justification for keeping this trait in our selection index when we’re having internal discussions about how to define the breeding goals each year.”
Although this underlines the role genetics can play in decreasing the incidence of POP, she says genetics alone won’t solve the issue at a heritability of 35%.
“By definition, 65% of the phenotypic variation in POP is caused by environmental factors. Just because we’re making noise about the importance of developing genetic solutions, it doesn’t mean the rest of the industry is off the hook,” she says. “We still need research into mycotoxins, nutrition, management, and other environmental factors.”
That’s where Phase III comes in. Phase II provided a better understanding of what genes are involved so they can then be traced back to figuring out what types of biological pathways might be involved, Dunkelberger explains. Phase III will take a deeper look at how genetics and management can work together to reduce POP. One objective of Phase III is to validate that breeding values for POP (developed using purebred data) are also predictive of susceptibility to POP for crossbred females (TN70s) in a commercial setting. Additional objectives include estimating the effect of parameters measured during late gestation on susceptibility to removal due to POP. Another student from Iowa State, Tricia Veldhuizen, is currently collecting these data on-farm as part of a summer internship experience with Topigs Norsvin.
“If you know the biological pathway, then you have much more of an idea of how to target your management recommendations,” she says. “For instance, one of the genes that Bhatia identified was a calcium receptor. We were excited about this finding because it validated work from our nutrition team regarding the importance of calcium level, and the ratio of calcium with other minerals, in susceptibility to POP.”
Read the full journal article in Frontiers in Genetics here.
Read More:
Study to Investigate Potential Mechanisms that Control Uterine Prolapse Susceptibility
Can Genetic Selection Lower Incidence of Uterine Prolapse in Pigs?
