Getting to know new low lignin alfalfa varieties (Chris Wacek-Driver)
Lignin is the primary fiber component that reduces fiber digestibility in ruminant diets. Because alfalfa contains high lignin concentrations (greater than 6.0 percent), alfalfa fiber digestibility is often compromised as compared to low lignin forages such as BMR corn silage (with a 2-percent lignin concentration).
As a result, plant breeders have sought to reduce lignin concentration in alfalfa – either through plant selection or by genetic engineering. Two companies have recently patented technology for low lignin alfalfa. Their hope is to provide greater flexibility in extending the harvest window, maximizing yield potential while maintaining quality.
The first company is Alforex Seeds, which is affiliated with Dow AgroSciences. Alforex has developed low lignin alfalfa through conventional plant breeding and selection. The seed is marketed under the name Hi-Gest®. It is available through distributors and dealers as well as the company’s website.
The second company is Forage Genetics International and its seed will be sold under the name HarvXtra™. HarvXtra was developed in partnership with the Samuel Roberts Noble Foundation and the U.S. Dairy Forage Research Center, along with Monsanto. A 2016 release is anticipated, pending deregulation from the USDA.
HarvXtra has been developed through genetic engineering. Essentially, developers “knocked out” or “turned down” the gene expression for key enzymes in lignin biosynthesis. Although the company is not selling the seed in 2015, some small acreage will be established on a few commercial dairies this year. HarvXtra will be stacked with the Roundup Ready® gene.
Research evidence and company claims suggest total lignin concentration is reduced by 7 to 15 percent over conventional alfalfa varieties. With genetically engineered low lignin alfalfa, the type and structure of lignin is also altered. Reductions and alterations in lignin concentration will vary greatly with cutting management, growing conditions and weather.
The proposed benefits of low lignin alfalfa may be different compared with the benefits of low lignin BMR corn silage.
Because harvesting alfalfa at the desired maturity is such a challenge, the proposed benefits of low lignin alfalfa include a more flexible alfalfa harvest window (adding 7 to 10 days), thereby maintaining quality during challenging harvest conditions. Additional benefits observed in research evaluations have included increased digestibility, improved animal performance, and/or potentially increased total alfalfa yield.
Since lignin serves as the “skeleton,” providing support to the plant as it matures, one question that invariably comes up is whether low lignin alfalfa will be more prone to lodging. Both companies claim, in field testing and plot research, reduced lignin has not significantly increased lodging as compared to conventional alfalfa varieties.
If low lignin alfalfa truly extends alfalfa cutting intervals, these varieties may increase long-term alfalfa stand yields. Research evaluating HarvXtra has explored reducing alfalfa harvest from a four-cut to a three-cut system. Due to increased plant reserves, less soil compaction and damage, and less plant stress, yearly plant tonnage actually increased. Limited data indicates a positive influence in stand persistence.
Alternatively, many alfalfa producers may choose to stay on the same alfalfa cutting schedule hoping to improve fiber digestibility.
Only a few peer-reviewed studies are available. In a USDA study, lambs fed HarvXtra had increased weight gains. Similar to BMR corn silage, lowering lignin should translate into increased NDF digestibility and enhanced animal performance, but field responses may be more challenging to observe due to common inclusion levels of alfalfa in modern dairy diets. Corn silage often comprises greater than 60 to 70 percent of the forage base, making responses to BMR corn silage easier to observe. In many situations, it is expected that the inclusion level of low lignin alfalfa in dairy diets will be appreciably lower than corn silage inclusion levels, making animal performance more challenging to observe.
In summary, benefits to low lignin alfalfa may include improved forage quality (if similar cutting schedules are maintained) or better labor efficiency (due to reduced cutting frequency). Agronomic data has shown increased yields with low lignin alfalfa when a cutting is eliminated, largely due to healthier plants. This strategy potentially reduces machinery and labor cost and field damage. Finally, data on animal performance is very limited.
Time and application of this new technology will prove its role in today’s dairy diets.