There is increased interest in having a single diet for dry cows rather than separate diets for far-off and close-up cows. Jim Drackley, professor of nutrition in the department of animal sciences at the University of Illinois, addresses three possible strategies for accomplishing this. The following answer is adapted from a paper he presented at the American Association of Bovine Practitioners conference in September.
Q: With a single dry period diet, how do I control for energy intake?
A: In light of the apparent desirability of feeding to allow cows to meet but not greatly exceed their requirements for energy during the dry period, there are at least three approaches that could be implemented to achieve this goal. The first is to feed cows only poor-quality roughages and other dietary ingredients that would minimize the potential for excessive energy intake. This is the concept that was the default management option on many farms several decades ago. However, the dangers are that excessive variation of ingredient quality may promote inconsistent intake of nutrients, the ration may provide imbalanced nutrient profiles, and such feeds may be contaminated with molds or toxins. This is not a desirable mind-set or approach and it will not be considered further here.
Two better approaches are:
- Limit-feeding: Formulating a diet of moderate energy density (1.50–1.60 Mcal NEL/kg DM) and limit-feeding it in amounts of dry matter (DM) that would meet the average Holstein cow or heifer requirement of 14–15 Mcal daily. Note that we are not advocating limiting cows below their requirements as we have done in some of our experiments (Dann et al., 2005, 2006; Douglas et al., 2006), although those cows almost always has the most favorable metabolic profile after calving. One study that implemented limit-feeding to requirements found favorable results (Holcumb et al., 2001), whereas a more recent study showed little difference between limit-feeding or ad libitum feeding (Winklemen et al., 2008). It should be noted in the latter study, however, that cow numbers were limited and three of nine cows assigned to the ad libitum (overconsumption) group developed health problems at calving and so did not contribute postpartum data to the evaluation.
Conceptually, limit-feeding is a workable method for controlling energy intake. In practice, however, it requires a high level of management to implement successfully. Limit feeding works only where cows are housed individually (rare) or where group-feeding systems allow an abundance of feeding space. Feed must be delivered over bunk space that is adequate to allow all cows access to feed. Implementation requires that dairy producers become as adept at managing feed bunks as beef producers are. The goal is to formulate rations for target DM intakes that would take cows at least 18 h/d to consume. In other words, dry cows should be fed to a clean bunk shortly before the next feeding. Given the dynamic nature of cows moving in and out of single-group dry cow pens or close-up pens, and perhaps variable total numbers of cows, management of limit-feeding often is more challenging on dairy farms that in beef feedlots.
- High-bulk, low energy diets: Formulating rations of relatively low energy density (1.30–1.38 Mcal NEL/kg DM) that cows can consume free-choice without greatly exceeding their daily energy requirements. The principle is to feed cows a diet of sufficient fiber (bulk) content that cows will only meet their requirements consuming all the DM they can eat. The target intake thus allows neither too much nor too little energy, but rather just the right amount to match requirements.
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.