Straw in dairy diets: A fad or necessity?
I recently returned from working with dairies in Romania, where I learned firsthand that balancing the need for effective fiber while preventing total mixed ration (TMR) sorting is not just an issue for North American dairies.
What I observed was a tendency to feed 12-14 lb. dry matter of extremely finely chopped corn silage (less than 0.5 in. of theoretical length of chop) while supplementing the ration with wheat straw that easily measured 4-5 in. in length.
The inclusion of long straw meant sorting was a common occurrence. When I suggested a longer chop length for corn silage (about 0.75 in.), the Romanian dairy producers expressed a legitimate concern about achieving adequate kernel damage, yet they seemed undaunted by the lack of TMR mixer capability to reduce the straw particle size to an acceptable length (1-2 in.).
This recent experience led me to re-examine the benefits and drawbacks of using straw in dairy diets.
Small-grain straw has become increasingly popular in dairy cattle diets primarily to: (1) provide a source of physically effective neutral detergent fiber (peNDF) that facilitates rumen mat development to stimulate rumination, (2) reduce ration energy density in groups that have a tendency for overconditioning (heifers and far-off dry cows) and (3) alter dietary cation:anion ratios in dry cow diets due to their generally low potassium content (Anderson and Hoffman, 2006).
Wheat accounts for the most readily available type of straw, which is reflective of a 2002 estimate of 62.1 million, 9.3 million, 6.1 million and 2.1 million metric tons of wheat, rice, barley and oat grains produced annually in the U.S. (Eastridge et al., 2009).
In a 2004 survey of high-producing Wisconsin dairies, Shaver and Kaiser (2004) reported that three of six dairies surveyed were feeding straw, two dairies were feeding straw to both the dry and lactating cows and one dairy was using straw only in dry cow diets.
Nutritionists and dairy managers have generally been feeding 0.5-2.0 lb. of straw to high-producing cows and up to 6-10 lb., or 30% of a ration, to dry cows (Holin, 2006).
An excellent survey of straw nutritive values from the University of Wisconsin (Anderson and Hoffman, 2006) found that the energy content of straw can vary from 22 Mcals to 54 Mcals of net energy for lactation per pound of dry matter. Only about half of the analyzed straw samples contained enough energy to support growth or milk production.
Potassium levels in straw range from 0.75% to 2.86%. Several of the sampled straw types would likely not improve the dietary cation-anion status due to their high potassium content.
Fiber digestibility in the Wisconsin report measured by neutral detergent fiber (NDF) digestibility (48 hours, % of NDF) varied from 20% to 57%.
In a Pennsylvania State University study (Varga et al., 2005), 10 wheat straw samples, two barley straw samples and one oat straw sample from various regions of Pennsylvania, Wisconsin, Michigan and Indiana were evaluated for digestibility in cannulated cows. The 48-hour dry matter digestibility of the straw samples varied between 25% and 40%.
The Penn State researchers also noted extreme differences in the pliability of the various straw types, with some so tough that the researchers found it painful to squeeze the samples in their hands, making them question the palatability and intake variation among cows fed those samples.
A number of nutritionists do their very best to avoid feeding straw due to the cost, sourcing difficulty, tendency to "gut-fill" without contributing much dietary energy and difficulty in achieving the desired particle size in many TMR mixers. They prefer the use of alfalfa or grass hay, wheat silage or byproducts such as whole cottonseed or almond hulls (Holin, 2006).
While digestible fiber sources like soybean hulls, wheat midds, brewers or distillers grains can serve to dilute dietary starch levels, they do not provide the peNDF level of straw that helps with rumen mat formation because the straw is dry, hollow, unfermented and offers superior rumen buoyancy.
Caution should be exercised when using dietary straw to help prevent ruminal acidosis. Research from Canada (Beauchemin and Yang, 2005) demonstrated that increasing the peNDF content of high-corn silage diets increased chewing time; however, increased chewing time did not necessarily reduce ruminal acidosis.
They suggested that formulation models that predict rumen pH should include both peNDF and fermentable organic matter intake.
This has also been observed in alfalfa-based diets (Poore et al., 1991) when chopped wheat straw was fed at 0%, 1.0%, 1.9% and 2.8% of the diet. The dietary forage NDF was held constant at 20-22%, while starch was allowed to increase linearly from about 25% to 30% with increasing levels of straw.
In this study, dry matter intake and milk yield were not affected by straw addition, but 3.5% fat-corrected milk linearly decreased with straw addition because the higher starch level linearly decreased the milk fat proportion.
These studies point out the importance of monitoring not only peNDF, cud chewing and sorting activity but also rumen starch fermentability (which, with ensiled corn, is known to be a moving target).
Researchers at the Miner Institute (Cotanch, 2010) voiced another concern with straw regarding the wet growing season in 2009 that appeared to cause many wheat straw samples to test positive for mycotoxins.
A number of straw samples at the Miner research farm from both large and small bales exhibited levels of deoxynivalenol of 2.0-3.0 parts per million. The researchers calculated that this level alone in the straw equated to about 0.5-0.8 ppm in the total TMR, although their closeup dry cow TMR actually tested higher at 1.4 ppm of deoxynivalenol.
Based on feeding recommendations, that level could pose a nutritional or health problem, particularly in dry and transition cow diets.
Wisconsin researchers (Anderson and Hoffman, 2006) pointed out that dust and dirt that accumulate before or during harvest most likely account for a wide variability in ash content of straw samples. They can also be a source of molds and other aerobic spoilage organisms that may grow on straw with pockets of elevated moisture from improper harvest and storage.
The Bottom Line
It is undeniable that some nutritionists have successfully fed high-quality straw in dairy cow diets lacking effective fiber. However, variation in straw nutrient content, possible mycotoxin contamination and issues with achieving a consistent, desired particle length to prevent sorting can make it a challenge to feed straw.
It is recommended that straw be tested as frequently as other feedstuffs given its inherent variability. Nutritionists and dairy producers may be able to avoid the cost and inconvenience of straw by paying close attention to forage particle size during harvest and storage of the primary forage sources.
Anderson, T., and P. Hoffman. 2006. Nutrient composition of straw used in dairy cattle diets. University of Wisconsin Extension Focus on Forage. Vol 8. No. 1.
Beauchemin, K.A., and W.Z. Yang. 2005. Effects of physically effective fiber on intake, chewing activity and ruminal acidosis for dairy cows fed diets based on corn silage. J. Dairy Sci. 88:2117-2129.
Cotanch, K. 2010. Straw, toxins and NDFD ... Related? The William H. Miner Agricultural Research Institute Farm Report. March.
Eastridge, M.L., P.B. Bucci and C.V.D.M. Ribeiro. 2009. Feeding equivalent concentrations of forage neutral detergent fiber from alfalfa hay, grass hay, wheat straw and whole cottonseed in corn silage based diets to lactating cows. Animal Feed Science & Technology 150:86-94.
Holin, F. 2006. Rationing straw. Hay & Forage Grower Magazine. September.
Poore, M.H., J.A. Moore, R.S. Swingle, T.P. Eck and W.H. Brown. 1991. Wheat straw or alfalfa hay in diets with 30% neutral detergent fiber for lactating Holstein cows. J. Dairy Sci. 74:3152-3159.
Shaver, R., and R. Kaiser. 2004. Feeding programs in high producing dairy herds. Proceedings of the Tri-State Dairy Nutrition Conference, Ft. Wayne, Ind. p. 143-170.
Varga, G., V. Ishler and P. Anderson. 2005. Dairy feeding - The last straw. Pennsylvania State University Dairy Digest.
This article was originally published in April 2012 Feedstuffs issue, and is reproduced with their permission.