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Sow Prolapse Syndrome: 13 Potential Causes

In the past four years, sow prolapse syndrome has been a growing problem for hog production systems across the U.S. Unfortunately, no definitive causes or treatments have been found. Jeremy Pittman, a veterinarian for Smithfield Foods, wants to raise awareness of the problem and to pose a call to action to the industry so producers can coordinate efforts to determine cause and resolution.


In late 2012, Smithfield got reports from sow farms in its north region of increasing cases of sow prolapses, says Pittman. The prolapses were a combination of rectal, vaginal, and uterine. They resulted in increased sow mortality, loss of unborn piglets, and increased preweaning mortality.

Pittman talked to others in the industry and heard familiar stories. “It was apparent that this increase in prolapses was being seen by veterinarians across the country,” he says.

A sow prolapse working group was formed by the American Association of Swine Veterinarians (AASV), and research on potential causes was shared.

smithfield data

Data was studied for 104,000 sows on 36 farms in Smithfield’s north region from 2008 to 2016. Results show that from 2008 to 2013, 2% of sows were removed annually for prolapse. This jumped to 3.5% from 2013 to 2016. The biggest increase was in uterine prolapses.

Of all prolapsed sows, 9% were culled, 28% died, and 63% were euthanized. 

“We have seen farms with as much as 25% to 50% of the sow mortality due to prolapses,” says Pittman.

Most prolapses are at farrowing or immediately following. The incidence of prolapses is highest in January, February, and March; it is lowest in June, July, August, and September. 

potential causes

Pittman has a few theories on the causes. “These are only opinions and should be evaluated,” he cautions. “The incidence of prolapses is historically very low and, therefore, difficult to study.”

The causes are listed below and are in a general order of importance or likelihood, says Pittman. 

1. Mycotoxins in feed 

The mycotoxin zearalenone can cause prolapses in swine in addition to other reproductive problems. However, feed samples from the affected Smithfield region did not find zearalenone as a cause.

Phytoestrogens from plants (such as clover, alfalfa, and soybeans) can cause prolapse. “Has something changed in soybean farming or postharvest processing to meal to increase the level of phytoestrogens in that product?” asks Pittman. 

2. Hypocalcemia 

Hypocalcemia is associated with uterine prolapse in dairy cows due to a dysfunction in calcium metabolism, dietary calcium levels, or a calcium-phosphorous imbalance. Prolapse in cows most closely resembles the syndrome in sows. 

“This is one area that needs to be explored as a potential risk factor,” says Pittman. “Maybe it is related to the trend to have more prolific sows while feeding the same base nutritional requirements.”

Recent industry changes to diets (including grind size, phytase use in sows, and feeding distillers’ dried grains with solubles) could be predisposing sows to hypocalcemia. However, Smithfield did a six-month trial of removing phytase from rations on half the system’s sow farms and saw no improvement in prolapse. 

3. Disease pressures 

Anything causing increased abdominal pressure can predispose pigs to prolapse, such as coughing, huddling, and piling. In the Smithfield sow cases, respiratory distress was not associated with prolapses, and many of the most severely affected herds lacked signs of any disease, reports Pittman. Piling of sows was not a factor in these units.

4. Abdominal issues 

Do automated feeding systems in farrowing barns allow too much intake by lactating sows? Does the decreased grind size of sow diets result in increased fermentation? Do alternative ingredients lend themselves to digestive changes? “We are seeing increased prolapses without automated feed delivery or ad-lib feeding in farrowing,” says Pittman.

5. High-density diets 

Diets high in starch and lysine have been associated with increases in rectal prolapses. It is not clear why this is the case, says Pittman. 

6. Vitamin deficiency 

Early findings from Iowa State University and the AASV show lower vitamin E levels in prolapsed sows compared with controls from the same farm. It is unclear yet if this is significant, says Pittman. Low levels of vitamin D in humans are associated with weakness of the pelvic floor muscles and uterine prolapse. 

7. Genetics 

Genetic predisposition is a risk factor for prolapses in pure-line breeds, says Pittman. “In our system, we have not seen a clear case of genetic influence. In fact, our most consistently and severely affected farms are a mix of multiplication and commercial herds.”

One herd experiencing a high incidence of prolapses was purchased in 2014 from a company with a different genetic supplier, he says. “Prior to 2014, the farm did not have excessive levels of prolapses, and it was only after feed formulation and manufacturing were taken over by our system that the farm experienced a significant increase in prolapses.”

The strongest argument against a genetic cause is the widespread incidence across production companies, genetic companies, sources, and lines, he says. 

8. Constipation 

Lack of adequate water and low-fiber diets can lead to constipation, straining, and increased prolapses. “We assessed fecal consistency in prolapsed sows, and constipation was an associated risk,” says Pittman. “Adding fiber to sow diets might be an area for further research.” 

9. Parity 

Older sows are at risk for prolapse postfarrowing due to loss of uterine and muscle tone. “In our cases, the increase is seen in all parities,” says Pittman. 

10. Housing 

It has been theorized that a lack of exercise in crate housing might contribute to increased risk of prolapses. Yet, Smithfield has experienced an increase of prolapses even on farms that have switched to group housing, says Pittman. 

11. Oxytocin and assisted farrowing 

Could excessive oxytocin use at the time of farrowing cause prolapses? “In most of our cases, prolapsed sows did not receive any treatment prior to prolapsing, including oxytocin, and they were not assisted with farrowing,” he says.  

12. Tail docking 

Docking tails too short can result in damage of the nerves near the anal sphincter and can cause rectal prolapse in growing pigs. “We measured tail length of prolapsed sows and found it not to be associated with prolapses,” says Pittman.

13. Larger litters 

Large litter sizes or large pigs predispose sows to uterus and abdominal pressure and excessive duration of farrowing. The increase in litter size of the swine industry could be a risk factor. This needs to be studied, says Pittman.

call to action

Pittman wants the swine industry to work together on this problem. There is no funding for research yet, he says, but the National Pork Board has expressed interest. 

“The sow prolapse syndrome we have experienced over the past four years has been frustrating and difficult to manage,” says Pittman. “We have made very little, if any progress, in understanding the causes, and the incidence continues to increase year by year. There is very little hope in the near future of solving the problem, unless there is increased awareness, focus, and a collaborated effort.

“We will increase our diagnostic efforts this year and try to determine any cause-and-effect relationships,” he says.

Pittman thinks the cause is likely with feed, ingredients, or ingredient nutrient value, feed contaminant, or formulation.

“Some universal change that the swine industry made unknowingly in the fall/winter of 2012-2013 has affected the physiology of the sow,” he speculates.


Jeremy Pittman, DVM

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