Feeding straw to dry dairy cows has become a popular strategy to decrease dietary energy content and increase the bulk fill of the ration. The key reasons for doing this are to maintain pre-calving dry matter intake and to keep the rumen expanded to avoid a displaced abomasum post-calving.
Interestingly, as straw has been utilized as a feedstuff in dry cow rations, dairy nutritionists are finding a place for it in lactating cow rations. Straw is being fed to lactating cows to add physically effective neutral detergent fiber (peNDF) to the ration. Just as blood meal provides a high amount of protein, straw provides a high level of peNDF in a tight package. Physically effective NDF is defined specifically as the fraction of fiber that stimulates chewing and contributes to the floating mat of large particles in the rumen. A recent sample of chopped straw that we analyzed with the Z Box had a physical effectiveness factor of 0.61 and a peNDF of 51.9 percent. This was compared to 34.3 percent peNDF for corn silage chopped at ¾-inch theoretical length of cut. In this example, chopped straw would provide about 51 percent more peNDF than corn silage per pound of dry matter.
As a source of peNDF, straw is fed to promote good rumen function and to increase rumen pH by stimulating cud chewing. Straw is also fed to help raise low butterfat test and to improve feed efficiency by moderating high dry matter intake (DMI) with bulk fill.
Often the dairy nutritionist struggles to achieve a healthy level of peNDF in the ration. There can be several reasons for low levels of ration peNDF including high-quality low-NDF forages, finely chopped forages, low-quality forages that need to be fed in limited amounts and NDF supplied by high amounts of non-forage fiber sources (NFFS) in the ration. Examples of NFFS include distillers grains, brewers grains, soybean hulls, corn gluten feed, citrus pulp and beet pulp. Non-forage fiber sources are fed to replace forage when dealing with low-quality forages or limited forage inventories. Feeding NFFS allows the nutritionist to decrease the amount of forage in the ration while keeping starch levels under control. Non-forage fiber sources are normally competitively priced as compared to other feed ingredients, often leading to a high level of inclusion rates in dairy rations. While these feedstuffs are high in NDF, they do little to provide the peNDF cows need to stimulate good rumen function. When feeding very digestible high-quality forages or finely chopped forages, straw may be added to the ration in order to decrease rate of passage and allow for more complete ruminal digestion of the feed. Additionally, raising peNDF of the ration with straw may also increase fat corrected milk.
Due to the drought that producers have experienced in the upper Midwest this past year, hay and haylage supplies are limited. Prices of NFFS are high and supplies are also limited. With these conditions nutritionists may find straw to be a necessary and cost-effective ingredient in dairy rations.
Although straw may fit in many rations, care should be taken when utilizing it. The slowly digested fiber (the key reason that straw is utilized in dry dairy cow rations) could be a problem in lactating cow rations. If adequate amounts of peNDF can be obtained without straw, feeding it may not be the best approach, as milk production may be limited by the addition of straw. It is well recognized that increasing the dietary concentration of high NDF forages with low NDF digestibility decreases milk production. The impact could be even greater for high-producing dairy cows. Researchers at Michigan State University demonstrated that high-producing cows have bigger increases in milk production than lower producing cows when rations with higher fiber digestibility are fed. The implication here could be greatly decreased peak milk when straw is included in the ration of dairy cows.
Lack of dietary peNDF is not the only reason why cows have elevated DMI. Before adding straw to moderate DMI, dairy nutritionists should evaluate if the diet could be too low in available carbohydrates that are fermented to propionate in the rumen. Reduced ruminal propionate production can cause cows to eat more feed in an effort to meet their energy demands. In this case adding readily available starch sources such as bakery byproducts, high moisture corn or finely ground corn will increase ruminal propionate production and lower DMI. When readily available starch sources are lacking, adding straw to the ration will not raise milk production and in many cases will not moderate DMI. Kendall and Combs (2004) showed that increasing straw from 8.5 percent of DMI (about 4 pounds) to 16.0 percent of DMI (about 8 pounds) only moderated intakes by 1.8 pounds while drastically decreasing milk production by 6 pounds Although the feeding rates of straw in this instance were extreme, they demonstrate that the addition of straw does not moderate intake as much as we might think, but can dramatically decrease milk production.
Book values for straw should not be used when formulating rations. Due to the high variability in straw quality, Anderson and Hoffman (2006) recommend that straw be tested by wet chemistry methods for at least DM, crude protein, NDF, NDF digestibility, fat and ash in order to calculate an accurate energy estimate. They reported straw analyses to range from 20.53 - 40.76 percent NDF digestibility and 16 - 90 relative feed quality (RFQ). Straw samples analyzed from June to December of 2007 by Dairyland Laboratories, Inc., Arcadia, WI, also showed high variation in nutrient composition (Table 1*). This amount of variation could cause nutrition modeling programs to have large errors in predicted allowable milk when significant amounts of straw are used in the ration. Additionally, straw that is moldy should never be fed to lactating dairy cows.
Dairy rations should provide a healthy range of NDF from forage (19-24 percent of dietary DM). The ration should also be checked regularly with a Penn State Particle Separator or a Z Box to ensure that there is enough effective fiber to promote good rumen function. The ration should always be formulated and managed to minimize sorting. Straw should be processed prior to feeding and needs to be chopped to 2 inches or less in order to minimize sorting. When straw is fed to provide peNDF this becomes critical. If sorting occurs and the cows do not eat the straw, the issues that it is being fed to address often become worse.
With its inclusion in many dry cow diets, straw has become a readily available ingredient on many dairy farms. As feed costs have increased, many nutritionists are allowing straw to least-cost into lactating cow rations. Straw can be beneficial to feed as a part of the lactating cow ration by providing peNDF that is necessary for good rumen health and optimizing production efficiency. However, dairy nutritionists should carefully consider if the forages and other ingredients will provide adequate amounts of peNDF without the addition of straw to the ration. Not all rations necessitate using straw and feeding it in cases where it is not needed may decrease milk production. PD
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Specialist for Vita Plus
In what circumstances (if any) would you recommend dairy producers not consider including straw in dairy diets?
When dairy rations do not have sufficient levels of physically effective fiber it can be provided by including straw. However, most rations will not benefit from feeding straw.
Because feeding forages with slow fiber digestibility to high-producing cows almost always reduces milk production, you should evaluate your dairy’s situation before feeding straw.
Straw should not be fed if the dairy has enough forage that can provide the required physically effective fiber.
Straw should not be fed if it cannot be processed to a length of 2 inches or less to avoid sorting.
Straw should not be fed until it has been analyzed by wet chemistry methods.
Straw should not be fed to reduce dry matter intake without first ensuring the diet has adequate starch and sugar. Researchers at Michigan State University have suggested that a lack of fermentable carbohydrates, not a lack of physically effective fiber, is what causes cows to overeat.
Straw should not be fed to raise milk fat without first limiting sources of rumen available polyunsaturated fat. Metabolites of polyunsaturated fat have been shown to drastically depress milk fat.
Stacy W. Nichols and Dr. Silvia G. Onetti for Progressive Dairyman