A Late-Finisher Enemy


Microbiologist Connie Gebhart oversees Lawsonia serology testing in University of Minnesota"s Veterinary Diagnostic Laboratory. Technician Benjawan Wijarn studies a sample for Lawsonia intracellularis antibodies.

It"s a disease that affects nearly every farm, yet it often goes unrealized even after it strikes. It severely depresses average daily gain and feed efficiency, but it typically garners little attention compared to highly visible diseases, such as porcine respiratory and reproductive syndrome or porcine circovirus associated disease. However, in today"s scenario of high feed prices, that may be about to change.

Subclinical ileitis a nearly invisible form of the disease   can result in very real performance losses all the way to market. Just how big can these losses be? A 2005 study found subclinical infections reduced average daily gain by 38 percent and negatively impacted feed efficiency by 27 percent.

"It"s definitely not what you would want when feed prices are going up," says John Deen, DVM, University of Minnesota swine researcher. "This often unseen form of ileitis is one piece of the puzzle that producers need to be concerned about when trying to reduce anything that contributes to worse performance and overall attrition."

Clinical signs:  A poor indicator

Since it is caused by the prevalent Lawsonia intracellularis organism, experts agree that subclinical ileitis is a universal concern. Although affected pigs often appear normal, the disease can be economically devastating.

This was evident in the 2003 National Swine Disease Impact Study, underwritten by an animal-health consortium. Even with relatively low feed prices at the time, producers reported that clinical ileitis cost $5.34 per head, on average. Perhaps more surprisingly, however, participants pegged subclinical ileitis costs at $5.19 per head, reflecting an insight into the disease"s costly hidden form.

To get an updated and comprehensive view of the risk that the ileitis pathogen poses, University of Minnesota and Elanco Animal Health researchers collaborated on a major serology study. Veterinarians collected blood samples from more than 5,000 pigs, representing 174 different pig flows across the United States. The samples were submitted to the University of Minnesota"s Veterinary Diagnostic Laboratory for testing using the immunoperoxidase monolayer assay testing method, which is able to detect even low levels of a pig"s immune response.

Deen presented the study"s findings at this year"s annual meeting of the American Association of Swine Veterinarians. Some key points included:

  • 94.3 percent of the pig flows that showed no clinical signs of ileitis tested positive for Lawsonia intracellularis and were classified as having subclinical ileitis.
  • 69.6 percent of the flows found to be sero-negative for Lawsonia intracellularis at 18 weeks of age were found positive between 21 and 27 weeks.
  • Disease status and seroconversion remain highly variable from farm to farm.
  • Clinical signs of ileitis are a poor indicator of infection and subclinical ileitis.

"This study doesn"t answer all of our questions about how a pig"s immune system reacts to Lawsonia infection," Deen says, "but it does reiterate the need to learn more about it, since the majority of farms do experience this infection."

No farm is immune

Having a general idea of when a herd is likely to seroconvert may be useful in fine-tuning the timing of ileitis control protocols, Deen points out. Unfortunately, that"s often a moving target. "We don"t know how stable the seroconversion point is. There seems to be some variability due to season and other factors," he notes.

Pig age may be one of the variables. According to Connie Gebhart, microbiologist and director of the University of Minnesota"s Veterinary Diagnostic Lab, that"s not entirely surprising. "This serology study reconfirms that pigs can test positive for antibodies to Lawsonia at any time, including late in the finisher   putting pigs at risk for poor health and performance."

Contrary to what some may think, pigs don"t always become immune to ileitis as they near market age. In fact, the study illustrates just how vulnerable older pigs are to subclinical ileitis after 12 weeks of age   just when feed efficiency gets worse even in healthy animals.

"Residual maternal immunity may protect young pigs, but that dissipates after a while," Gebhart says. "As maternal immunity to ileitis goes down, pigs become more susceptible to the Lawsonia in their environment."

As for protecting pigs from subclinical ileitis at the farm level, conducting serology tests may not always be practical. "Since seroconversion can change from group to group, producers should just assume their pigs are going to contract ileitis at some time," Gebhart says.

Greg Armbruster, a veterinarian and technical consultant with Elanco, says producers may not always be focused on long-standing threats such as subclinical ileitis, but that could be a costly oversight. "With health challenges such as PCVAD and PRRS, it is easy to forget about subclinical ileitis. But in
terms of lost pig performance, that"s a mistake, especially with today"s high feed prices."

He advises producers to think about how they can best control subclinical ileitis and protect pig performance all the way to market. "We know clinical signs are a poor indicator of subclinical ileitis, so it"s a matter of using the best tools available to manage the ongoing threat to pig health and performance."

Finding hidden areas that rob your herd of average daily gain and feed efficiency will increasingly determine how wide your profit margins are in the future. Now is the time to start looking.


In a study of Lawsonia intracellularis prevalence in U.S. swine herds, results showed the pathogen affects pigs of all ages. The highest percentage of positive farms actually involved older pigs. Nearly 70 percent of pigs that tested negative for the pathogen at 18 weeks old were later found to have it and were classified as having subclinical ileitis.


As pigs get bigger, they start eating more feed, but conversion becomes increasingly less efficient. At 12 weeks old, feed efficiency is near 2.1, but at 27 weeks it"s around 3.3 or more. That"s a bad time for subclinical ileitis to occur, but according to a recent study, probably the most likely time.



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