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Ongoing grass forage research

Jim Paulson, Dairy Extension Educator

Published in Dairy Star June 23, 2012

Alfalfa is the primary forage fed to lactating dairy cows; however, there is renewed interest in utilizing grass forages in lactating dairy cow diets, particularly because of farm sustainability issues such as nutrient management, less erosion and feeding advantages while potentially lowering feed costs. This is because including grasses in the forage increases the amount of digestible NDF in the forage of the diet while adding effective fiber and more rumen mat. Grasses will also help forage dry faster, utilize nitrogen from the alfalfa, and add to yield potential. As we have reported earlier, data thus far would indicate that mixed stands of alfalfa and cool season grasses can compete or exceed alfalfa alone for yield and quality. Perceived yield and quality is generally lower for grass species compared to legumes. However, forage quality of grass silages at forage testing labs compares very well with legume silages indicating more focus on quality by producers harvesting as silage. Grasses may also compliment diets with high levels of co-products from the ethanol and food industries better than legumes because grasses are generally moderate in crude protein (CP) compared to alfalfa and most co-products contain a significant amount of CP. By lowering diet CP levels, we improve nitrogen utilization and lower nitrogen excreted and potentially lost to the air or to leaching.

When harvesting grass, several key points are useful. If harvesting as haylage, the ideal moisture is 65%, much like corn silage. Because early maturity grasses are low in fermentable sugars, it is highly recommended to use an inoculant at ensiling. If you are baling dry hay or putting up baleage, we recommend using as wide a swath as possible, up to 80% of haybine width, to dry faster. This reduces respiration losses which results in higher quality forage. Wider swaths also have more uniform drying from top to bottom of the swath. This makes more uniform baleage when there are less moisture differences within a swath. These recommendations apply as well to alfalfa-grass mixtures.

Tall fescue and meadow fescue are two grasses that we are researching more at the University of Minnesota. With newer varieties developed, we have observed increased palatabilities, winter survival and most importantly, forage quality. Forage maturity also matches better with alfalfa for harvesting in mixed stands. Newer varieties of meadow fescue and tall fescue will contain approximately 50 to 55% NDF with an in vitro 48 hours NDF digestibility of 65 to 75% of NDF when harvested at the boot stage.

In a recent study, University of Wisconsin researchers (Verbeten et al., 2012) found that the NDF digestibility of tall and meadow fescues were similar to the in vitro NDF digestibility of alfalfa. To test this approach, they ran a study in which they used high quality tall fescue or meadow fescue silages as a source of digestible fiber in dairy cattle diets. A control diet and two diets with either tall fescue or meadow fescue (Table 1) were fed to high producing early lactation cows. The control diet, formulated with corn silage and alfalfa silage as the only sources, was designated as a 'hot' diet that was high in NFC and low in NDF (Alf/CS). Tall fescue or meadow fescue was used in the test diets to replace about a third of the corn silage and alfalfa (Alf/CS/TF or Alf/CS/MF).

Replacement of about a third on a dry matter basis of the corn silage and alfalfa silages with the fescue silages raised the total fiber content and lowered the dietary NFC of the diet. This reduced the amount of ruminally-digested NFC and increased the amount of ruminally-digested NDF by adding the fescues to the diets. Cows fed the diets with tall fescue or meadow fescue produced the same amount of 3.5% fat corrected milk as cows fed the diet with alfalfa and corn silage as the only sources of forage. Adding grass to the diets did not depress feed intake. Including grass in dairy rations appears to be a feasible strategy to reduce the NFC level of early lactation diets and increase levels of fiber without reducing milk yield.

Table 1. Composition of test diets containing either alfalfa and corn silage (Alf/CS), or alfalfa and corn silage and tall fescue (Alf/CS/TF) or alfalfa and corn silage and meadow fescue (Alf/CS/MF).

Feed Alf/CS Alf/CS/TF Alf/CS/MF
  -------- % of diet DM --------
Corn silage 26 17 17
Alfalfa silage 26 17 17
Tall fescue silage 0 17 0
Meadow fescue silage 0 0 17
High moisture corn 26 25 26
Protein/mineral 22 24 23

Source: Verbeten et al., University of Wisconsin, 2012.

High quality, well managed grasses have potential as a source of highly digestible fiber for high producing dairy cows. 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. Perhaps the greater opportunity for grasses in dairy rations is as a feedstuff that is high in digestible fiber and low in NFC. There appears to be a need for these types of feedstuffs when excellent quality corn silage and alfalfa are the core forages in dairy rations and grass provides greater nutrient contribution than does straw.

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