Improving Pig Livability by Understanding Pelvic Organ Prolapse

Researchers seek to lower pig mortality with a three-point perineal scoring system.

by Zoe E. Kiefer, Jamie M. Studer and Jason W. Ross

pie chart sow mortality rates

Throughout the last decade, rising sow mortality has become a major concern within the US swine industry, with a substantial proportion of it due to pelvic organ prolapse (POP) incidence.

In 2018, an industry-wide survey conducted by the Iowa Pork Industry Center revealed that POP accounted for 21 percent of all sow mortality. At the time and because existing literature on POP in sows was limited, our team of researchers began designing and conducting studies aimed at identifying potential factors contributing to POP in late gestation sows.

To identify sows with a greater risk of experiencing POP, our team developed and tested a three-point perineal scoring system based on visual evaluation of the perineal region of late gestation sows.

chart sow perineal scores

In brief, a perineal score (PS) of 1 (PS1) indicates a low risk for POP and has little to no protrusion, redness, and swelling of the perineal region. By comparison, a PS of 3 (PS3) indicates a high risk for POP and has moderate to severe protrusion, redness, and swelling of the perineal region, and potentially the beginning of a prolapse.

This scoring system has been tested and validated in several research studies, and sows assigned PS3 are more likely to subsequently experience POP than PS1-assigned sows. Additionally, perineal scoring can aid in the identification of sows at high risk and compare them to sows at low risk for POP, and in the future, help identify targets for mitigation strategies.

More information on this perineal scoring system can be found on the Improving Pig Livability website (www.piglivability.org). Multiple studies have been conducted to explore similarities and differences in sows with different perineal scores.

Markers of Inflammation: The high risk for POP phenotype is characterized by obvious signs of swelling and inflammation, which led our team to evaluate circulating markers of inflammation1. Complete blood counts were analyzed on sows with either low or high risk for POP. Decreases in mean platelet volume, lymphocytes, and monocytes were observed between sows at high risk compared to those at low risk for POP, indicating there is an inflammatory response in PS3 sows. Additionally, c-reactive protein, haptoglobin, tumor necrosis factor alpha, and creatine kinase were measured in sows at varying risk for POP, but no statistical differences were observed. However, we did observe lipopolysaccharide (LPS)-binding protein (LBP), a proinflammatory cytokine, to be increased in PS3 sows compared to PS1 sows.

Metabolite Differences: To evaluate differences in circulating metabolites, serum was collected from sows assigned either PS1 or PS3 during late gestation, and then subjected to metabolomic analysis via gas-chromatography mass-spectrometry. In total, 82 metabolites were identified as significantly (P < 0.05) different between low- and high-risk sows2. Metabolites such as L-methionine, L-alanine, 2-aminobutanoic acid, lactic acid, and D-glucose were more abundant in PS3 sows compared to PS1 sows. D-Fructose is of particular interest, as it was 5.3-fold more abundant in PS3 sows and had a 78.5 percent accuracy as a potential POP risk biomarker. Additionally, we observed an increased abundance of 2-aminobutanoic acid, a butyric acid derivative associated with inflammation, in the circulation of PS3 sows compared to PS1. Butyrate is a metabolite produced by gut microbiota that is involved in the regulation of host metabolism and health. Steroid Hormone Variations: Steroid hormone profiles were evaluated on PS3 and parity matched PS1 sows1. Circulating concentrations of androstenedione, androsterone, estrone, and estradiol (E2) were increased in PS3 sows compared to PS1 sows. Specifically, E2 promotes pro-inflammatory responses and has been observed to be increased in humans with reproductive disorders, including POP. Differences in the vaginal microflora have been associated with alterations in steroid hormones and/or immune system modulation.

piglets looking at camera
Photo Credit: artbyPixel/iStock / Getty Images Plus photo

Microbial Community Changes: Many reproductive disorders have been associated with fluctuations in the microbiota of livestock and humans. Our team conducted two studies to evaluate the vaginal microbiota of sows at variable risk for POP. The initial study utilized sows across two production systems, in two different states. We observed differences in 24 operational taxonomic units (OTUs), representing individual microbial species, between sows with high POP risk compared to parity-matched sows with low POP risk2. This study was replicated using sows from two different farms in close proximity to one another and from the same production system. Again, we observed differences in 51 OTUs between PS1 and PS3 assigned sows3. Interestingly, similar trends in specific microbes such as Streptococcus, Clostridium, Treponema, Veillonella, and others were observed between the two studies. These similarities help improve our understanding of “healthy” microbial communities versus communities experiencing dysbiosis and also help us identify specific microbes as potential targets for mitigation strategies.

Mitigation Strategies: Results from the initial studies improved our understanding of potential factors contributing to POP such as differences in vaginal microbiota and steroid hormones. This information led us to conduct studies to evaluate potential mitigation strategies aimed at reducing the incidence of POP in sows. Our team has tested two mitigation strategies involving the use of antibiotics, although neither was effective in reducing POP incidence rates. Interestingly, both studies revealed that PS3-assigned sows have a statistically greater percentage of stillborn piglets compared to sows assigned PS1. This indicates that PS3-assigned sows represent opportunities to incorporate targeted strategies to reduce the overall incidence of piglet stillbirths. Results from these mitigation studies are in preparation for publication in peer-reviewed journals.

Future Directions: Our future directions include evaluating fecal microbial communities, trace minerals, circulating analytes, and continuing to develop and test mitigation strategies with the overall goal of reducing POP-related sow mortality.


1. Kiefer, Z. E. et al. Circulating biomarkers associated with pelvic organ prolapse risk in late gestation sows. J. Anim. Sci. (2021). doi:10.1093/JAS/SKAB207

2. Kiefer, Z. E. et al. Vaginal microbiome and serum metabolite differences in late gestation commercial sows at risk for pelvic organ prolapse. Sci. Rep. 11, 6189 (2021).

3.Kiefer, Z. E. et al. Vaginal microbiota differences associated with pelvic organ prolapse risk during late gestation in commercial sows. Biol. Reprod. 2021, 1–17 (2021).