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Could a little grass in your ration be a good thing?

PD Editor Karen Lee Published on 03 February 2010
hay field

Grasses have been replaced by corn silage and high-quality alfalfa in Midwest rations, but Dr. David Combs, Department of Dairy Science, University of Wisconsin – Madison, says there might be a place for them in the diet again.

“I’m not going to talk about replacing high-quality alfalfa or corn silage,” Combs says. “Grasses can be a commodity feed that fits in rations like soy hulls. It gives us some flexibility.”

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Grasses have been known to have some challenges. They are higher in fiber and if not managed correctly, can lead to problems. When looking for maximum yields per acre, grasses don’t come close to corn silage. Pure alfalfa stands are easier to manage, but if you select the right grasses that mature late and are cut early, there can be benefits.

“You’ve got to manage grasses just like you do everything else to make them work,” he says.

Agronomic advantages

Grasses aid in faster and more consistent drydown, can help to manage winterkill, and provide additional manure management options.

Grasses can serve as cover crops to boost yields in the first year of a three- or four-year alfalfa rotation. Work by University of Wisconsin Forage Specialist Dan Undersander in using ryegrass as a cover crop established that planting two to four pounds of grass yielded an additional 1/2 to 1 ton per acre of dry matter. Yet Undersander also found that when planting at rates higher than four pounds per acre, the grasses challenge the alfalfa seedlings.

Perennial grasses, like orchardgrass, can add a substantial increase of neutral detergent fiber (NDF) to the forage yield. However, if you delay harvest by a week or two, the fiber really starts to increase. Late- maturity grasses should be planted and then they should be harvested early, Combs recommends.

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Alfalfa grass mixtures must be managed carefully, he says. “The timing of first cutting is very important. There is a lot of variability in terms of maturity in grass varieties and I’d rather cut the stuff in the vegetative stage than when it’s headed out.”

At similar stages of maturity, grasses have higher NDF values than alfalfa, but the fiber is more digestible. Typically grasses were penalized for their higher fiber content, but the newer relative forage quality index (RFQ) recognizes the higher proportion of digestible fiber in grasses and the potential impact that grass fiber has on intake and milk yield.

Nutrition advantages

The nutrient profile of high- quality grass silage complements the excesses and deficiencies of rations formulated with excellent quality corn silage and alfalfa. Grasses are to be viewed as a balancing ingredient in dairy rations today and not as a forage replacement, as they have in the past.

Previous grass-based studies compared a diet formulated with alfalfa to a diet formulated with an equivalent amount of grass. Of course, the grass-based diet had higher amounts of fiber, which limited dry matter intake and in turn milk production. Therefore, alfalfa was considered superior forage for high-producing cows.

Instead, grass forage should be considered as a feedstuff that could balance a low-fiber, high-starch diet. Grasses have a higher proportion of digestible fiber. Currently, producers are using wheat straw to gain rumen scratch, but that’s undigestible fiber. Unlike straw, grasses will also provide energy.

Grasses can be a good fit in high corn silage diets that are high in non-fiber carbohydrates (NFC) and low in NDF. Replacing part of the corn silage and alfalfa in a ration with high-quality grass fiber could shift the proportion of fermented energy from NFC to NDF while not reducing the overall digestibility of the diet, Combs says. This shift in fermentable components would be expected to provide a more steady supply of fermentable substrate to rumen microbes, which could in turn help stabilize the production of rumen acids and minimize the occurrence of ruminal acidosis.

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“Lameness is one issue we see a lot more of today than we did 10 to 15 years ago,” Combs says. “A lot of it is diet-driven.”

Lameness is caused by a lot of different things, including low-fiber diets, more than 40 percent NFC in the ration, finely processed feeds, sorting and slug feeding. “That’s why we’re adding wheat straw to high corn silage diets,” he says.

“If I’m going to reduce acidosis or manage lameness I need to watch what’s going on in the rumen,” says Combs. Protein and NFC should contribute 75 percent to the total organic matter fermented in the rumen and NDF should be at 20 percent.

In a recent study, Combs compared a “smoking hot” corn silage and alfalfa ration with a treatment ration where one-third of the corn silage and alfalfa was replaced with a high-quality Italian ryegrass silage. By adding the Italian ryegrass, Combs reduced the amount of ruminally digested NFC and increased slightly the amount of ruminally digested NDF. Milk production stayed up and he witnessed a significant increase in fat test and a 3.5-pound increase in fat-corrected milk with the grass ration. In addition, no lameness was detected, but Combs also attributed that to new facilities with no overcrowding.

He mentions more studies are needed, but considers the addition of grasses into the ration as going in the right direction thus far. The fiber in early maturity grasses is more digestible than alfalfa fiber, and when grasses are used to replace alfalfa fiber, milk production and intake of high-producing cows do not appear to be affected.

What to plant

Combs recommends using tall fescue and orchardgrass because the new varieties of those grasses are standing head and shoulders above the rest. Italian and perennial ryegrass can really eat up manure and make for good annual cover crops, he adds. Brome and timothy grasses, however, largely fall off the table because they don’t yield like the newer varieties.

The website – www.uwex.edu/ces/forage/resdata/grass_table.htm – can help with selecting grass varieties for fields in the Midwest. Producers should use yield, persistence, late maturity and establishment as their top criteria in choosing the grasses to plant, Combs says.

The ideal stand will be planted at 30 percent grass to balance out alfalfa. That will leave enough legumes to fix the nitrogen for grasses to grow. If more grasses are planted, additional nitrogen may be needed. PD

David Combs is aDairy Science Nutrition Professor withUniversity of Wisconsin. Email David Combs.

Karen Lee
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