er 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 