There are two forms of ileitis — the acute form which strikes late finishers hard, with severe bouts of bloody diarrhea and sudden death — and the chronic form, which causes infection and 1-2 weeks of diarrhea.

The chronic form of ileitis represents a big threat to pork producers trying to combat the number one enteric disease of grow-finish pigs.

Elanco Animal Health scientists say a subclinical form of the chronic form of ileitis is of growing concern because, if left untreated, it may depress growth without any evidence of clinical signs (diarrhea or gaunt appearance). It can only be confirmed by laboratory tests.

A serological survey conducted by the Agriculture Department's National Animal Health Monitoring System found that 96.2% of tested U.S. herds are positive for Lawsonia intracellularis, the bacteria that causes ileitis. But only 37% of those herds appear to be clinically infected.

That leaves a large gap of herds that may be subclinically infected with ileitis, but may go undetected or undiagnosed.

More Damage Found

In a new study, Swedish researchers have reported that subclinical bouts of ileitis can produce damage that begins earlier and lasts longer than previously thought.

A study by M. Jacobson at the Swedish University of Agricultural Sciences looked at 13 herds of young grower pigs, nine poor performers with and without diarrhea, and four herds with average to good performance and no diarrhea.

Postmortem examinations discovered the good-performing pigs were indeed healthy. But the poor-performing pigs concealed numerous pathogens, ileitis being the most common.

In the poor-performing herds, researchers found 67% of sick pigs harbored Lawsonia intracellularis.

But more significantly, scientists found Lawsonia in 41% of the poor-doing but seemingly healthy, diarrhea-free pigs.

Findings on intestinal lesions were similar, with 63% of the poor-doing but outwardly healthy pigs having microscopic lesions.

“This study emphasizes what we've known for a long time,” says Tom Marsteller, DVM, Swine Technical Services Manager with Elanco Animal Health. “Even though grower pigs may appear outwardly healthy, they may be infected with Lawsonia and suffering from the subclinical form of ileitis.”

Also, based on the Swedish study, average daily gain is 25% less in pigs with subclinical disease including ileitis, than in healthy pigs.

Earlier Studies

In an earlier study published in Veterinary Microbiology, Roberto Guedes, Federal University of Minas Gerais, Brazil, reported that following an outbreak of ileitis, intermittent shedding of Lawsonia lasted up to 12 weeks, confirming long-term, persistent bacterial infection, without any apparent clinical signs of the bacteria.

Another study showed that shedding can take place for an indefinite period, spreading infection to penmates.

Data from Minnesota swine veterinarian Nate Winkelman indicated that pigs that were challenged with ileitis, but recorded no difference in fecal scores from unchallenged pigs, had lower gains and feed efficiency.

“So if your only measure is whether you see diarrhea, you may be missing something,” says Marsteller. He says producers may need to weigh pigs and check records to assess gains over a period of time to find out if they are missing subclinical infection with ileitis.

Disease management is one goal of Advanced Ileitis Management, Elanco's new ileitis control program. Marsteller explains that Tylan can help improve growth through ileitis prevention.

Tylan also works to manage pig flow, reducing lightweights and variation.

And it improves economic returns by controlling all forms of ileitis, including the subclinical form that can reduce profits by $3-3.50/pig, says Marsteller.

For prevention and control of subclinical ileitis, Marsteller recommends using Tylan Premix at 100 g./ton for 21 days.