Genetic basis of pelvic organ prolapse in the sow

Sow mortality has been a major growing concern for the swine industry, attracting the attention of producers, researchers and industry experts. The trend of increasing mortality rates is being observed globally, posing a serious production and welfare problem for the global swine industry. More importantly, the economic losses associated with sow mortality are substantial. Such losses could be attributed to the opportunity cost of losses of weaned piglets, loss of culled sows or replacement of sows in the production system. Furthermore, such an increase in sow mortality can drastically affect employee morale on the farm and raise employee welfare concerns.

There are a multitude of interacting and time varying factors that are leading to an increase in sow mortality. Nutritional imbalances, changes in management practices, the environment, infectious and non-infectious stressors, and reproductive complications are some factors that may contribute to this growing concern.

One such factor is pelvic organ prolapse, which is characterized by the loss of support from the tissues and muscles of the pelvic floor. This leads to the pelvic organs falling out of their normal position, resulting in protrusion of the pelvic organs, including the rectum, urethra, bladder, cervix, uterus, or vagina. Typically, vaginal, uterine and rectal prolapse are the most prevalent types seen in sows, either in combination or individually.

An industry-wide survey reported the role of multiple factors contributing to the increased risk of POPs in sows and genetics was sought to be one of them. However, there have been conflicting reports in previous years regarding the role of genetics in the susceptibility of sows to POP.

A recent study used pedigree-based records and reported that 22% of phenotypic variation in POP was due to genetics. Our study used the same dataset but advanced further to evaluate and understand the role of genetics in sow susceptibility to POP using genomic information.

This study was conducted using data collected on 30,429 purebred female records (calving and culling) from two multiplier farms located in the Midwestern United States, collected between 2012 and 2022. Of these records, information was available on the genotype of 14,186 sows. Sows were genotyped for 48,075 genetic markers throughout the genome. The overall incidence of POPs was 7.1% for dead and cull sows and was defined as the presence of vaginal, uterine or rectal prolapse or any combination present as it was difficult to distinguish between the three conditions for a farm employee. farm. Overall analyzes were performed as through and parity analyses. Statistical analyzes were conducted to estimate the heritability of POP susceptibility both between and within peers and the genetic correlates of POP susceptibility. Furthermore, a so-called genome-wide association study was performed to identify genomic regions associated with POP susceptibility, followed by functional genomic analyzes of these regions to identify potential genes and biological processes associated with POP susceptibility.

POP susceptibility has been confirmed to have a substantial genetic basis in this population and herds. This indicates that it can be selected against our herds to increase the survival of our sows. POP susceptibility has also been confirmed to have a similar genetic basis in different parities. Genome-wide association studies revealed six regions of the genome that were associated with POP susceptibility, but together they explained only 9% of genetic differences between sows. This means that there are many other genomic regions that contain genes associated with POP susceptibility but have small effects. Functional analyzes also provided detailed insights into several biological processes associated with POP susceptibility, including the role of collagen, estrogen receptor gene, and glycoproteins that are important for calcium/phosphorus homeostasis.

While there is no silver bullet, susceptibility to POP can be reduced by genetic selection because it is substantially heritable, at least in some populations and herds. Therefore, using POP data from such herds, breeders can choose to reduce the POP susceptibility of their lines using procedures similar to those used to select, for example, litter size. Furthermore, with further research, knowledge of the biological pathways discovered to influence POP susceptibility can be used to develop recommendations or targeted management interventions to reduce the incidence of POP in herds worldwide.

Bhatia, V., Stevens, T., Derks, M., Dunkelberger, J., Knol, E., Ross, J., and Dekkers, J. (2023). Identification of the genetic basis of pelvic organ prolapse in the sow. Frontiers In Genetics, 14. doi: 10.3389/fgene.2023.1154713

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