ARS | Publication request: Influence of Bt Transgenes on Cell Wall Lignification and Digestibility of Maize Stover for Silage

Submitted to: Crop Science
Publication Acceptance Date: March 29, 2004
Publication Date: August 25, 2004
Citation: Jung, H.G., Sheaffer, C.C. 2004. Influence Of Bt Transgenes On Cell Wall Lignification And Digestibility Of Maize Stover For Silage. Crop Science. 44:1781-1789.

Interpretive Summary: Genetically modified (GM) crops are being adopted by farmers at an accelerating rate. Corn hybrids protected by the Bt toxin gene against the European corn borer insect pest now account for 29% of U.S. corn acres planted and have reduced insecticide usage for control of this pest in corn production. Two recent reports have suggested that Bt corn plants contain more of a natural compound known as lignin. Lignin in plants limits digestion of plant fiber by cattle. If higher levels of lignin are present in Bt corn plants, then it would be expected that the feeding value of corn silage made from Bt corn hybrids would be reduced for dairy and beef cattle. Because corn silage is a major cattle feed, such a result would have serious implications. To test the validity of these claims about increased lignin in Bt corn, 12 commercial hybrids (six Bt hybrids and their genetically identical non-GM counterparts) were compared in a field study at four locations around Minnesota. Using three different methods for measuring lignin, no consistent differences were found for lignin concentration of the Bt corn plants compared to their respective genetic counterparts. Total corn silage yield and concentrations of protein, starch, and fiber were not altered by the presence of the Bt gene. Fiber digestibility was also not different between Bt and normal corn hybrids. The presence of the Bt gene in GM corn hybrids did not alter lignin content or other corn characteristics. Farmers should have confidence that Bt corn hybrids can be used for dairy and beef production without impacting milk and meat production.

Technical Abstract: There have been inconsistent reports that maize (Zea mays L.) hybrids with the Bacillus thuringiensis (Bt) cry1 Ab transgene contain more lignin than non-Bt hybrids of similar genetic background. Our objective was to evaluate the impact of the cry1 Ab transgene on lignin concentration (using three different assays), yield, and forage quality traits of maize. Replicated trials were conducted at four locations in Minnesota with 12 commercial hybrids (three MON810 and three Bt11 cry1 Ab transgene event hybrids, and respective near-isogenic controls). Whole plants and the fourth elongated, above-ground internodes were harvested at silage maturity. Samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), acid detergent fiber, 24- and 96-h in vitro ruminal NDF digestibility, and lignin (acid detergent, Klason, and acetyl bromide). European corn borers (Ostrinia nubilalis) were not controlled and damage was limited to the non-Bt hybrids, averaging 1.5 internodes plant-1 with tunnels. Environment and environment by hybrid interactions impacted all measures of maize performance and quality, but comparisons of non-Bt/Bt hybrid pairs, for both whole plants and internodes, found no consistent differences in yield, nutrient content, in vitro ruminal NDF digestibility, or lignin concentration. Differences in lignin concentration (for all three analysis methods) were infrequent, small in magnitude, and inconsistent between a few non-Bt/Bt hybrid pairs at individual locations. Two non-Bt/Bt hybrid pairs did not differ in lignin concentration at any location. Contrary to some earlier reports, presence of the cry1 Ab transgene did not alter lignin concentration or other forage quality traits of maize stover in commercial maize hybrids.