Salmonella typhimurium is an organism that takes advantage of stressed pigs. Pig rearing today is complicated by economics, nutrition, labor and health challenges

March 15, 2010

4 Min Read
Salmonella awaits opportunity to strike stressed pigs

Salmonella typhimurium is an organism that takes advantage of stressed pigs.

Pig rearing today is complicated by economics, nutrition, labor and health challenges. One lesson reinforced to us is that health trumps all of these.

An example is Salmonella typhimurium — an opportunistic organism that takes advantage of stressed pigs and causes disease.

Salmonella typhimurium is more commonly found today in pigs than the pig-specific strain of Salmonella choleraesuis. Salmonella typhimurium can infect many mammals, including humans, and is widespread.

Case study No. 1

A producer who purchases pigs from a sow cooperative called concerning diarrhea in weaned pigs recently placed in one of two separate site nurseries and then moved to multi-site finisher barns. The 2,400-head finishers are filled in one day. The client was blaming bad corn quality for the diarrhea, but efforts to improve feed quality weren't working.

Walking through the youngest two finishing groups, I observed that 10-20% of the pigs had a watery, yellow-tinged diarrhea. Mortality was 1% each on pigs placed two and four weeks ago. Many pigs were gaunt and depressed. Rectal temperatures indicated fevers of 104-105°F.

We collected some tissue samples and submitted them to the diagnostic lab. On postmortem exam, a portion of the small intestine was inflamed and reddened, but most of the large intestine was reddened with portions of it thickened, causing a severe enterocolitis. The thick segments were opened and the surface lining had a gray, rough appearance with some evidence of blood on the surface when the necrotic material was scraped away. Mesenteric lymph nodes were also swollen.

The diagnostic lab found a heavy growth of Salmonella typhimurium in the large intestine and lymph nodes, but no ileitis or F-18 E. coli. An antibiotic sensitivity assay evaluated which antibiotics to use for treatment because salmonella bacteria is often resistant to common antibiotics.

The producer chose to mass medicate the pigs for five days with a water-soluble antibiotic and also use injectable antibiotics on those pigs showing signs of gauntness and dehydration. Most recovered within a week.

Corn used for feed contained a high level of mycotoxins, but also ventilation settings of both barns had been reduced to decrease propane costs when these groups were started on feed. This led to a moist, cold floor environment.

Those two stressors resulted in the pigs becoming infected with Salmonella typhimurium.

Case study No. 2

A producer with a 1,000-sow, farrow-to-finish operation was getting complaints from the contract finishers about a high percentage of pigs demonstrating signs of “straining to defecate” within two weeks of delivery to the finisher barns. The producer manages both the sow unit and nursery, but all finishing is contracted. The nursery manager was concerned with the number of rectal prolapses he had been repairing in the older nursery pigs.

During a farm visit, 15% of newly weaned pigs had diarrhea. By the fourth week in the nursery, the diarrhea ended and the oldest pigs appeared very healthy. Yet they were experiencing a 4% incidence of rectal prolapses.

I recommended that tissue samples from the younger nursery pigs be sent to the diagnostic lab for testing. Salmonella typhimurium was cultured from the large intestine.

The finding of Salmonella typhimurium in the younger nursery pigs is likely the cause of rectal prolapses seen in the older nursery pigs. The nursery manager reports that most of the prolapses heal on their own. The irritation to the bowel can cause rectal strictures and may subsequently lead to straining when those pigs attempt to defecate, as seen in the finisher pigs.

The owner decided to start using an oral salmonella vaccine on the pigs in the farrowing house. Vaccinating the pigs at this age allows immunity to be established before weaning.

Management practices were upgraded to include strict all- in, all-out movement of nursery pigs, along with improving washing and disinfecting procedures of the rooms. The diarrhea in the early nursery period has not reappeared, and rectal prolapses in finisher pigs have not been reported since these changes were made.


Salmonella typhimurium can be a zoonotic disease and can pose a health risk to caretakers. Salmonella is also the second-leading bacterial cause of food-borne human illness. Pigs can shed the organism for several months, and become a chronic source of reinfection.

Consult with your veterinarian about the risk of infection to your pork production system.

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