Low-lignin alfalfa improves digestibility
By KAREN SCHWALLER
ORANGE CITY – When it comes to feeding dairy cows, Bruce Anderson believes producers cannot afford to use outdated forage types any more than they can afford to use outdated genetics in their herd.
The extension forage specialist with the University of Nebraska-Lincoln spoke at the I-29 Moo University Winter Workshop Series, which took place last week in Orange City.
Anderson said forage composition and cost have a major impact on dairy milk production and profits. There are characteristics to consider for the four main forage types (corn silage, sorghum silage, cereal silage and alfalfa) when selecting hybrids and varieties, with the goal of increasing milk production.
He added some of the new low-lignin alfalfas on the market today are a “big step forward” in terms of opportunities to improve feed quality and, in turn, increasing milk production.
What is lignin?
Anderson described lignin as a complicated compound; so complicated that rumen microbes and other enzymes in the digestive system have a difficult time breaking it down in order to gain access to valuable starches and release nutrients.
“It’s almost completely indigestible,” Anderson said. “It’s basically what wood is made out of, and we don’t get many nutrients out of wood.”
As an example, he said lignin in the cell walls act as rebar. There are digestible components of a cell wall, but when lignin binds onto the compounds in the cell wall, it reduces the ability of the microbes to gain access to potential nutrition from the other compounds within the cell wall.
“As a plant gets more mature, the plant produces more lignin, making it less and less possible for the rumen microbes to get the nutrients out of those fiber components,” Anderson said, adding fiber is extremely important to the digestive system of a dairy or beef cow.
If lignin were reduced enough so that all alfalfa now fed in the U.S. to the beef and dairy industry were allowed to improve digestibility of cell walls by 10 percent, he said the overall value of the beef and milk produced in the U.S. would increase by $350 million.
“You’ll never pocket all of that yourself, but you can certainly get your portion out of it by feeding these kinds of alfalfas,” he said.
He went on to say that if cows can digest more of what they eat, there will also be less manure, saving in terms of manure processing and costs associated with it.
Going further, Anderson said when cows chew corn in silage, it may result in some kernels being missed altogether in the chewing process. As a result, corn kernels may enter the digestive system whole or almost whole, leaving the enzymes to break down hard, protected cell walls. With high amount of lignin in corn silage, the digestive process is greatly slowed.
He recommended producers seek out newer characteristics when selecting forage types.
Some factors to consider are:
– High concentrations of neutral detergent fiber (NDF) reduce intake and lower energy due to relatively low digestibility of NDF.
– Higher NDF digestibility usually provides more energy and milk production potential.
– Brown mid-rib (BMR) results in less lignin so fiber digestibility and intake increases, along with lodging. Anderson suggested including lodging resistance when selecting for the BMR trait.
– A soft kernel trait is demonstrating increased starch digestibility and higher feed efficiency, resulting in more milk and more butterfat.
– High-grain hybrids may produce more milk if both fiber and starch digestibility are high.
– The percentage of NDF and NDF digestibility are as important in sorghum as in corn, since sorghum silage tends to have more fiber than corn silage.
– The BMR-6 trait can enable sorghum silage to have energy value similar to corn, though lodging is a concern, especially with tall varieties and hybrids.
– The “Brachytic dwarf” trait results in shorter, leafier plants that yield as much as taller types. When combined with the BMR trait, lodging is usually overcome.
– Cracked berry. Anderson said sorghum grain has a hard seed coat that can cause grain to pass completely through the digestive system. Silage must be processed adequately or harvested prior to the hard dough stage in order to access and utilize the starch in the berry.
– Awns (prickle-like extensions) on barley, triticale and wheat can cause discomfort or injury, resulting in reduced intake and performance. Varieties are available that lower that risk)
– High rates of nitrogen fertilizer are often used to obtain high yields from cereals, increasing the risk of lodging.
– Highest protein and digestibility occurs at the boot stage for wheat and barley silage, though yields are relatively low and moisture is high. Anderson said maximum yield of dry matter and digestible dry matter usually occur at mid-dough for all cereals.
– Barley has superior forage quality among the cereal species. Within barley varieties, semi-dwarfs tend to be better than two-row types, which are better than six-row types.
Anderson said to find varieties with less lignin using both conventional and GMO breeding techniques. Alfalfas can be harvested at conventional growth stages for higher quality forage, or can be allowed to grow slightly longer between cuttings for higher yields with the same forage quality.
– Higher digestibility. He said those varieties are like reduced-lignin varieties, but are selected specifically for higher digestibility regardless of lignin concentration.
– Future varieties of alfalfa are expected to become available with the PPO (red clover enzyme) trait that is expected to reduce post-harvest protein degradation in alfalfa silage.
– Future varieties of tannin-containing alfalfa may increase the amount of bypass protein in alfalfa and may also reduce the risk of bloating.
– Genetic traits for better leaf retention and later flowering are being explored as new ways to increase alfalfa forage quality.
As new varieties become available, Anderson said it is critical that these differences can be measured accurately for proper forage selection and ration development. He added for many of the forage quality improvements, RFV (relative feed value) tests are inadequate, especially for improved digestibility. RFQ (relative forage quality) tests were developed to overcome many of the deciding factor limitations that came before it.
“Even more advanced analyses, such as TTNDFd (total tract NDF digestibility) are becoming available to provide even better results,” said Anderson.
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