Here’s some good news for those of you who planted a herbicide-tolerant corn hybrid this spring.

Two out of three studies reported in the May Journal of Dairy Science suggest hybrids that tolerate glyphosate — the active ingredient in Roundup herbicide — don’t adversely affect feed intake or milk production.

The studies were conducted at the University of Illinois, the University of Nebraska and Purdue University. They are the first such published studies to explore the effect of glyphosate-tolerant corn on dairy cattle performance.

In all three studies, a portion of the diets fed to lactating cows contained corn silage and corn grain from transgenic hybrids tolerant to glyphosate or nontransgenic control hybrids with a similar genetic background. Two of the studies also used commercially available conventional hybrids in the diets.

The glyphosate-tolerant hybrids tended to decrease dry matter intake in all three studies — some to a greater extent than others. The most significant decrease occurred in the Nebraska study. That study showed cows fed a glyphosate-tolerant hybrid ate about 6 pounds less dry matter than cows fed the nontransgenic control hybrid. The dry matter intake of cows fed the glyphosate-tolerant hybrid also was about 7 pounds less, on average, than two conventional hybrids.

The primary reason why the cows ate less glyphosate-tolerant silage in the Nebraska study was because it had a higher dry matter content at harvest. "The problem with our study was certainly the fact that the (glyphosate-tolerant) silage was too dry compared (to) the other silages," says Rick Grant, president of the W.H. Miner Agricultural Research Institute in Chazy, N.Y, and formerly with the University of Nebraska at the time of the study.

Meanwhile, the Illinois work showed only a 2-pound decrease in dry matter intake by cows fed a glyphosate-tolerant hybrid compared to those fed a control hybrid. Furthermore, the dry matter intake of cows fed the glyphosate-tolerant hybrid was nearly identical to that of cows fed a conventional hybrid.

The study at Purdue University showed virtually no decrease in dry matter intake by cows fed a glyphosate-tolerant hybrid compared to the control hybrid.

Glyphosate-tolerant hybrids did not hurt milk production in the University of Illinois and Purdue University studies. However, the Nebraska researchers observed a 7- to 9-pound reduction in milk yield from the glyphosate-tolerant hybrid. Again, that may be because the glyphosate-tolerant silage was too dry at harvest.

These studies support previous research findings that show the performance of poultry and hogs is not affected by glyphosate-tolerant hybrids. However, because these studies are the first to explore the impact of glyphosate-tolerant hybrids on dairy cattle performance, more work is needed.