Bt corn not to blame for pseudopregnancy rates, ISU says

Ames, Iowa -Researchers at Iowa State University (ISU) have concluded that genetically altered corn isn't to blame for higher-than-normal pseudopregnancy rates in sows on five Iowa farms.

An Iowa farmer first raised concerns that the Bacillus thuringiensis(Bt) corn he had been feeding his sows might have had an impact.

Bt corn contains a gene from a soil bacterium that helps the plant combata yield-reducing pest, the European corn borer. Following publicity aboutthe situation, a few other farmers said they had fed Bt corn and also hadreproductive problems in their swine operations.

Some of the producers met with veterinary and plant pathology expertsat ISU. As a result of the meeting, Dr. John Carr, assistant professor ofdiagnostic and production animal medicine, visited five farms where reproductiveproblems occurred. In addition, two farms where Bt corn was fed but no fertilityproblems existed were evaluated.

The visits revealed that all the farms fed the animals a combinationof Bt and non-Bt corn varieties. Several different Bt corn hybrids wereused in the feeds.

Carr, Drs. Thomas Carson, professor of veterinary medicine, and GaryMunkvold, associate professor of plant pathology, concluded there was nolink between the pseudopregnancy reproductive problem and the feeding ofBt corn.

Pseudopregnancy is a condition in which a sow or gilt has a delay inits normal estrus recycle period. During this delay, many behavioral orphysical signs typical of pregnant animals may be exhibited, but no pigsare ever delivered.

The occurrence of a pseudopregnancy most often is related to managementor proper pregnancy testing. Another reason may be the presence of estrogen-likecompounds produced by fusarium, a fungus found in corn.

Some kinds of fusarium infect corn kernels and can, under certain conditions,produce mycotoxins.

The ISU researchers said zearalenone, a mycotoxin that acts like estrogen,is the one most often associated with pseudopregnancy. Corn from the fivefarms studied was tested for the presence of mold spores. Fusarium moldswere found, but none of the corn samples contained any detectable zearalenone.

"It's been known for many decades that fusarium infection is verycommon in corn kernels," says Munkvold. "However, the presenceof fusarium does not necessarily mean that mycotoxins are present at harmfulconcentrations."

Bt hybrids typically have lower levels of fusarium, so the producersinvolved were surprised by the mold spores that were found.

"When insects feed on corn kernels, the kernels are more susceptibleto infection," Munkvold says. "Although Bt corn is not immuneto fusarium, it rarely has insect injury to the kernels, so the risk forinfection is reduced."

Carr said the cause of pseudopregnancy can be difficult to determine.

"Pseudopregnancy has been recognized for many years and is presenton pig farms throughout the world, irrespective of the type or consistencyof the feed being used," he adds.

Carr said a detailed examination of breeding management programs helpedresolve the problem on three of the farms involved. Problems on anotherfarm were resolved prior to the start of his investigation. The fifth operationclosed.

Two 750-sow units, which were not experiencing pseudopregnancy problems,also were examined over a six-month period while the animals were fed avariety of Bt corn. A normal farrowing rate of 82 to 84 percent was recordedwith no significant pseudopregnancy problems.

Munkvold says there is no evidence that feeding grain from Bt hybridsposes any danger to livestock. "Numerous feeding studies with a varietyof animals have been conducted and no detrimental effects have been observed,"he says.