Iowa State researchers have addressed concerns about genetically modified corn causing higher-than-normal pseudopregnancy rates in sows. After conducting research they have determined that Bacillus thuringlensis (Bt) corn is not to blame.

A gene from soil bacterium is added to corn to produce Bt corn. This gene helps to combat the yield-reducing European corn borer.

After conducting the research, John Carr, assistant professor of diagnostic and production animal medicine; Thomas Carson, professor of veterinary medicine; and Gary Munkvold, associate professor of plant pathology, concluded that the Bt corn did not cause the pseudopregnancy problems.

Included in the research were five farms experiencing reproductive problems and two farms where no fertility problems existed. All seven of the farms used Bt corn and non-Bt corn as livestock feed. Several varieties of Bt corn hybrids were used in the feed. The farms were located throughout the state.

“I’m happy to say that Bt corn itself doesn’t cause pseudopregnancy problems,” Carr said. “Pseudopregnancy has been recognized for many years and is present on pig farms throughout the world, irrespective of the type or consistency of the feed being used.”

Pseudopregnancy is a condition in which a sow has a delay in the normal estrus cycle. During this time the sows present signs of pregnancy without ever delivering.

Numerous things can cause the pseudopregnancy problems.

“It is fundamentally people,” Carr said. “They believe a sow to be pregnant when she’s really not.”

He also attributed the problems to “boars being overused, sows being moved too often or sows being too lean due to outdoor units.”

Another possible cause of pseudopregnancy is the presence of estrogen-like compounds called mycotoxins that are produced by the fungus Fusarium.

According to researchers, zearalenone is the mycotoxin that is most commonly associated with pseudopregnancy.

Samples of feed corn were taken and tested from all of the farms. Fusarium molds were found, but none of the corn samples contained any detectable zearalenone.

“It’s been known for many decades that Fusarium infection is very common in corn kernels,” Munkvold said. “However, the presence of Fusarium does not necessarily mean that mycotoxins are present at harmful concentrations.”

Carr said Fusarium is “a little like moldy bread. It is normally a storage issue.”

To resolve issues on the farms in question the researchers looked at reproductive problems that “are typical on a day to day basis,” Carr said.

“Detailed examinations of breeding management programs” helped explain the problems on three of the five farms. One of the farms fixed the problems prior to the investigation. The fifth farm closed due to economic reasons.

“It was disappointing to me personally to not have been able to solve his problems,” Carr said of the fifth farm. “There are still unanswered questions.”

A formal report about the investigation is expected to be published later.