To accomplish the goal of controlled energy intake requires that some ingredient or ingredients of lower-energy density be incorporated into diets containing higher-energy ingredients such as corn silage, good-quality grass or legume silage, or high-quality hay. Cereal straws, particularly wheat straw, are well-suited to dilute the energy density of these higher-energy feeds, especially when corn silage is the predominant forage source available. Lower-quality grass hays also may work if processed appropriately, but still may have considerably greater energy value than straw and thus are not as effective in decreasing energy density.
We are aware of no controlled data comparing different types of straw, but it is the general consensus among those who have years of experience using straw that wheat is preferred. Barley straw is a second choice, followed by oat straw. While reasons for these preferences are not entirely clear, wheat straw is more plentiful, is generally fairly uniform in quality, and has a coarse, brittle, and hollow stem that processes easily, is palatable, and seems to promote desirable rumen fermentation conditions. Barley straw lacks some of these characteristics. Oat straw is softer and as a result does not process as uniformly. In addition, oat straw generally is somewhat more digestible and thus has greater energy content.
It is critical that the straw or other roughage actually be consumed in the amounts desired. If cows sort out the straw or other high-bulk ingredient, then they will consume too much energy from the other ingredients and the results may be poor. A TMR is by far the best choice for implementing high-straw diets to control energy intake. Very few TMR mixers can incorporate large amounts of straw without pre-chopping and without overly processing other ingredients. Straw may need to be pre-chopped to 2-inches or less lengths to avoid sorting by the cows.
Based on our research and field observations, adoption of the high-bulk, low-energy TMR concept for dry cows might lead to the following benefits:
- Successful implementation of this program essentially eliminates occurrence of displaced abomasum. This may result from the greater rumen fill, which is maintained for some period of time even if cows go off feed for some reason, from the stabilizing effect on feed intake or through alteration of dietary cation-anion balances and potassium status (Janovick Guretzky et al., 2006; Janovick et al., 2011).
- Field survey data collected by the Keenan Co. in Europe (courtesy of D. E. Beever, Richard Keenan and Co., Borris, Ireland) indicate strongly positive effects on health. In 277 herds (over 27,000 cows) in the United Kingdom, Ireland, France and Sweden, changing to the high-straw low-energy TMR system decreased assisted calvings by 53 percent. In addition, the change decreased milk fevers by 76 percent, retained placentas by 57 percent, displaced abomasum 85 percent, and ketosis by 75 percent. Using standard values for cost of these problems, the average increase in margin per cow in these herds was $114 just from improved health alone. While these are certainly not controlled research data, they are consistent with the results in our research as well as field observations in the U.S.
- The same sources of observational data indicate that body condition, reproductive success, and foot health may be improved in herds struggling with these areas. A recent meta-analysis underway of our studies in this area shows that controlling energy intake decreases time to conception by 10 d compared with overconsumption of energy (Cardoso et al., 2011, unpublished data).
- Although data are limited, milk production appears to be similar to results obtained with higher-energy close-up programs (Richards et al., 2009; Vasquez et al., 2011). There is some evidence that persistency may be improved, with cows reaching slightly lower and later peak milk. Therefore, producers should be careful to not evaluate the system based on early peaks and should look at total lactation milk yield, daily milk, and, over time, indices of reproduction and other non-milk indicators of economic value.
- Straw and corn silage generally are lower in potassium and calcium, and thus help control the dietary cation-anion difference (DCAD) without excessive addition of anionic salt mixtures. Blood calcium concentrations decrease less when energy intake is controlled before calving (Dann et al., Janovick et al., unpublished data).
- The program may simplify dry cow management and ration composition in many cases.
- Depending on straw cost, rations based on corn silage and straw likely will be no more expensive than the average cost of traditional far-off and close-up diets, and could be cheaper where straw is plentiful. Remember that even when straw appears expensive, it is replacing something else in the diet so marginal cost is the key criterion. Furthermore, total DMI per cow may be lowered by addition of straw, so that feed cost per cow per day can actually be decreased substantially.