Fiber in reduced-lignin alfalfa is easier to digest, feeding trials show
Reducing lignin in alfalfa can improve fiber digestibility in cows and lambs by up to 10%, according to feeding trial results from Dave Mertens, U.S. Dairy Forage Research Center, Madison, WI.
Mertens and David Weakley, LongView Animal Nutrition Center, Gray Summit, MO, conducted trials using the genetically modified alfalfa. They determined that the animals digested an additional 10% of the feed's fiber and created less manure. That, of course, could increase milk production or provide the same amount of milk with less feed, Mertens suggests.
This type of alfalfa is a few years away from being in growers' fields. Lignin in today's alfalfas keeps plants upright but also lowers digestibility. Genes bred into current varieties could produce lower amounts of lignin, making the alfalfas more digestible but strong enough to stand.
Field trials have also been in the works to determine if the quality of reduced-lignin alfalfa will compare to that of current alfalfas — if its harvest were delayed 10-14 days. If quality stays the same, reduced-lignin alfalfa could reduce the number of cuttings needed and increase yield. Results were not available at presstime.
The reduced-lignin plants were grown in isolation by Forage Genetics, the company that developed Roundup Ready alfalfa. The Noble Foundation, which conducts forage improvement and plant biology research, was instrumental in “down-regulating” enzymes in the lignin pathway, Mertens says.
The down-regulating, he adds, lowered the activity level of two enzymes in two genes that control lignin. Plants developed with those altered genes were fed to six lactating cows and six young lambs.
“Everybody would like to have all the data with cows. But with cows you've got two disadvantages in evaluating how you've affected the plant. The first is that you can't feed the dairy cow an all-forage diet; you have to feed about 50% grain in the ration.” That dilutes results, he says.
The other disadvantage is that, many times, total mixed rations of forage and grain cause a negative interaction that lowers fiber digestibility. So young lambs, which can eat an all-alfalfa diet and have intakes as a percent of their body weights that are similar to those of lactating cows, were made a part of the study.
The researchers also studied how the level of feed intake affected digestibility. As animals eat increased amounts of feed, it passes through their digestive systems faster, which gives the feed less time to be digested. So they fed lambs to appetite, measured digestibility, then restricted their intake to a maintenance level.
“It was a very complicated set of experiments to try to address as many issues as we could that we thought might affect fiber digestibility in these alfalfas to verify that we improved it and were able to maintain that improvement when we put it into a TMR.”
After collecting refused feed and feces, the researchers calculated what the animals actually digested.
The study showed that both enzymes improved digestibility. It also served as a proof-of-concept type of experiment, Mertens says.
“For the first time we had two plants with specific and well-defined changes in lignin. The point of this research was to try to understand how lignin affects digestibility and how we can modify lignin, specifically to improve digestibility.”
Additional reduced-lignin alfalfa research will be reported as it's made available.