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Jazzed about low-lignin alfalfa

Woody Lane, Ph.D. for Progressive Dairyman Published on 24 May 2018
Jazzed about low-lignin alfalfa

Have you ever played jazz or listened to it? If so, you know that great jazz musicians play their instruments in all sorts of creative ways, and they are very good at using different techniques to get the same wild musical riff.

Well, this issue’s article is about a nutritional breakthrough in alfalfa. Our jazz musicians are alfalfa breeders. Instead of music, they play with genetic traits. And their notes – uh, traits – are about increasing fiber digestibility, specifically by reducing lignin.

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Why lignin?

Lignin? Here’s a quick overview. Plant fiber is composed of three main compounds: cellulose, hemicellulose and lignin. (There are lesser compounds like pectin, beta glucans, etc., but this month we’re interested in the big ones.) The bulk of fiber is made from cellulose and hemicellulose. These are primarily long fibrous strands.

Lignin is different. Its three-dimensional structure features extremely stable cross-linkages, like an angled truss in roof construction. Basically, lignin is designed to add strength and structural stability to the fiber. As forage plants grow larger and mature, the amount of lignin increases in the leaves and stems, which makes structural sense for the plant.

But lignin presents a nutritional problem: Its digestibility is zero. Although rumen microbes can ferment cellulose and hemicellulose and convert these molecules into nutrients for our animals, they are stymied by lignin. Neither the rumen microbes nor the host animal has enzymes that can break down those strong lignin bonds.

And as a plant matures, its fiber becomes more and more lignified. Nutritionally, there is an inverse relationship between lignin and fiber digestibility: the higher the lignin, the lower the digestibility of the fiber. It’s not a one-to-one relationship because the chemistry is rather convoluted, but it’s pretty close.

By the way, lignin is not a villain molecule with a black cape and a large mustache. It’s actually a critical player in plant physiology. In addition to adding structural stability, it improves the transport of water and minerals through the plant. It also helps limit the spread of pathogenic bacteria, thus reducing decay. Nonetheless, lignin certainly reduces the nutritional quality of the fiber.

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Genetic breakthrough

Now for the genetic breakthrough. Alfalfa is one of the most widely grown forages in the world, primarily for hay and silage but also for grazing. Its digestibility is greatly influenced by the digestibility of its fiber because the neutral detergent fiber (the main analysis of fiber) is generally 35 to 50 percent of its dry matter.

And fiber digestibility is greatly affected by the amount of lignin, which constitutes 5 to 9 percent of the entire plant’s dry matter and approximately 20 percent of the fiber.

Wouldn’t it be great if we could somehow reduce lignin levels while still maintaining yield? Well, this has happened. In the past two years, companies have released two new alfalfa cultivars definitely lower in lignin. These varieties are known in the field as, logically, “low-lignin alfalfas.”

Like our jazz musicians playing their instruments, geneticists have approached the lignin problem in different ways to reach the same results. One geneticist group developed the Hi-Gest variety using conventional breeding methods, using the old-fashioned techniques of crossing and selecting.

A second group developed the HarvXtra variety using GMO techniques. (This variety is also bundled and sold with the Roundup Ready gene, although these two traits are not genetically linked. The bundling was a marketing decision by the company.)

In either case, these varieties contain 10 to 20 percent less lignin than standard alfalfa varieties, which translates to an increase in fiber digestibility of 10 to 15 percentage units. There are lots of variation among research trials, but the basic pattern is good.

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When geneticists manipulate DNA, they say their target is either “up-regulated” (made more active) or “down-regulated” (made less active). Using their lingo, we can say geneticists modified alfalfa by down-regulating a couple of the enzymes involved in lignin synthesis. This means they shut off the genes that code for these enzymes, causing those metabolic pathways to slow down or come to a complete stop, kind of like the traffic jams we’ve all experienced. The alfalfa plants still produce some lignin, of course – otherwise they would melt down into the ground.

What’s in it for me?

So why are these low-lignin alfalfas important? Because the increased digestibility can be a real boon to livestock producers and also to hay growers.

First, the livestock perspective: Confinement dairy farms with high-producing cows feed huge amounts of grain. These dairymen need some roughage in the diet to prevent milkfat depression and other metabolic disturbances. They often rely on high-quality alfalfa as their fiber source, but any roughage can reduce the energy level of the entire diet.

The low-lignin alfalfas, however, give dairymen an option for adding roughage with slightly higher digestibilities, which can translate to 2-plus pounds of milk per cow per day. For a dairy milking 500 cows, that equates to a lot of additional milk every day.

Or in feedlots: Again, these operations push their animals for the highest daily gain possible and feed high-grain rations to do it. But like dairy farms, feedlots must include at least 10 percent roughage in the diet to reduce the problem of acidosis. Using the low-lignin alfalfas can translate to a slightly higher daily gain. As some folks like to say in Washington, D.C.: A billion dollars here, a billion dollars there – it all begins to add up.

There’s also a definite gain for farmers and ranchers who graze weaned lambs and stocker cattle on alfalfa fields. For animals grazing alfalfa as 100 percent of their diet, a 4 to 5 percentage unit increase in digestibility can have a major effect on daily gain.

If I owned these animals, I would definitely look to rent fields growing low-lignin alfalfa. Conversely, if I owned alfalfa fields, I might want to plant the low-lignin varieties to increase my market for hay and grazing.

Now let’s look at the hay growers’ perspectives. Alfalfa is the premier hay crop in the U.S. Throughout much of the country, alfalfa is grown in a four-cut system, which means four cuttings are harvested from a field every year, leaving enough time in the late summer and fall for the plants to prepare for winter. This system strikes a balance between plant yield and nutritional quality while still leaving enough carbohydrate root reserves to support healthy plants.

But the low-lignin alfalfas can change things in a very attractive way. Hay growers can wait an extra week before cutting and still obtain the same nutritional quality as before. Over the entire growing season, this becomes a three-cut system. Conversely, if they still followed a four-cut system, the nutritional quality at each harvest goes up. But delaying harvest for a week hugely increases yield. It also allows plants to build up their root reserves and thus be healthier and more persistent in the stand.

The low-lignin alfalfas allow a three-cut system to obtain the same nutrient quality as a four-cut system but with considerably higher yields, maybe 20 percent or more. A three-cut system also means fewer equipment trips across the field, less traffic stress on the plants, fewer chances for soil compaction, fewer open areas between plants and larger plants that better outcompete and suppress weeds.

There we have it: a nutritional breakthrough on a traditional forage – like a new jazz riff on an old standby tune. Genetics and jazz: Each gets results in complex and creative ways. But someday, I would like to see a research paper on lignin written in five-four time.  end mark

ILLUSTRATION: Illustration by Kristen Phillips.

Woody Lane, Ph.D., is a livestock nutritionist and forage specialist in Roseburg, Oregon. He operates an independent consulting business and teaches workshops across the U.S. and Canada. His book, From The Feed Trough: Essays and Insights on Livestock Nutrition in a Complex World, is available online. Email Woody Lane

Woody Lane
  • Woody Lane, Ph.D.

  • Lane Livestock Services
  • Roseburg, Oregon
  • Email Woody Lane, Ph.D.

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