April 28 2010 01:37 PM

After six years of limit-feeding research at Penn State, the system seems to get better with each study.

The authors are a post-doctoral researcher and professor at Penn State.

When limit feeding is initiated, heifers will be quite vocal for the first week. Vocalization virtually disappears 10 days after the program is implemented.

Limit feeding is an old concept that has recently generated new interest. Feeding high-concentrate, high-energy diets instead of traditional high-forage diets can improve feed efficiency, and research shows these diets can be limit fed without negatively impacting future productivity. Four full-lactation studies have shown that limit-fed, high-concentrate diets (actual diets varied greatly by study) yielded less manure - up to 40 percent less in some studies - with no differences in health, age at calving, body weight at calving, or first-lactation milk, fat, or protein yields.

When limit feeding, no free-choice forages are fed, and the balanced diet is typically fed once a day as a TMR. Nutrient specifications presented here are based on our current understanding of limit-feeding systems.

Heifers require a specific amount of crude protein daily, and total protein is just as important as the various protein fractions. In contrast to cows, research shows providing rumen undegradable protein (RUP) in addition to what is naturally found in feeds is of limited value to heifers. When high RUP feedstuffs are more economical than lower RUP feeds, they certainly can be used, but there is no benefit to using these feeds to boost diet RUP. In our studies, protein use was maximized when diets contained 14 to 14.5 percent crude protein.

Energy requirements are influenced by heifer size, growth rate, and environment and can be met in different ways. Diets can be formulated at variable energy densities and fed ad libitum. Alternatively, diets can be formulated at a fixed (generally higher) energy content and limit fed. Heifers should most often be fed enough energy to allow 1.75 to 2 pounds of gain per day.

Traditionally, high levels of fiber or low-quality forage were fed to control dietary energy; however, limit feeding high-concentrate, low-fiber diets effectively accomplishes the same goal. The neutral detergent fiber (NDF) requirements for growing heifers are not well established, but feeding NDF as low as 19 percent has not negatively affected heifer performance.

Research shows higher than "normal" concentrate levels can be fed without harm to the heifer. It is important to understand that if low NDF diets are used, the amount animals eat must be limited. There are no data to suggest that vitamin or mineral requirements are altered by limit feeding.

Feed ingredients for heifers should be selected on cost, availability, and nutrient composition. Much of the limit-feeding research conducted to this point has utilized corn and soybean meal to provide energy and protein. As the concentrate proportion of the ration increases, there is greater opportunity and flexibility for including cost-effective by-product ingredients.

Forage is an important consideration for limit-fed diets. Using lots of corn silage in limit-fed rations is possible; however, it requires careful monitoring of heifers because a considerable portion of corn silage is grain. Many rations in limit-feeding research have used corn silage as the principal forage, and no detrimental effects have been observed - even when corn silage was the only forage.

When feeding high levels of grain to heifers, limiting the amount of alfalfa hay may be necessary to maintain proper rumen function, especially if high-quality alfalfa is the only forage fed. Straw, corn stover, or other high-fiber materials can be incorporated into limit-fed diets. But, these feeds add no value to the diet and create more manure from the heifers.

Measure heifers. Measure body weights monthly, especially when beginning a limit-feeding program. The enhancement in feed efficiency is remarkable, and you probably will need to limit feed even more than you planned to avoid excessive growth rates.

Control group variation. In any group-housed heifer facility, minimizing variation in size and age within groups is important, and it remains important in a limit-feeding system. After 4 months of age, keep heifers in groups with less than 200 pounds (90 kg) of weight variation. Often this weight limit means ages range by no more than 2 to 4 months. After breeding, a weight spread of 300 pounds (136 kg) between animals in a group is acceptable.

Provide bunk space. In limit-feeding systems, heifers need 14 to 20 inches of bunk space per heifer as they progress from 4 to 22 months of age. Limit-fed heifers will not have access to feed at all times of day. Thus, all heifers in a pen must be able to eat at one time. Overly aggressive and timid heifers are very susceptible to over- or underfeeding when bunk space is limited.

Avoid straw and shavings for bedding. Limit feeding is based on meeting energy requirements through a producer-imposed restriction - not by gut fill limiting dry matter intake. Since gut fill and average daily gain potential will not be maximized, heifers will readily consume edible bedding. Eating bedding disrupts the intended balance of the limit-fed diet, and much of the gain in feed efficiency and reduced manure production is lost. Maintaining the balanced ration under limit feeding requires complete consumption of the diet presented each day without consumption of supplemental forage or edible bedding.

Transition to limit feeding. At the initial implementation of limit feeding, heifers will likely vocalize immediately prior to feeding, with the frequency and magnitude increasing toward the next few feedings. Research experiences are that this behavior diminishes and virtually disappears by 7 to 10 days after the start of limit feeding. This is due to a moderate reduction in rumen and gut size which is one reason for improved efficiency in limit-fed heifers.

The transition to limit feeding requires time and commitment similar to the time it takes to increase gut capacity after calving. As long as heifers are growing according to your goals and receiving a correctly balanced ration, they are being adequately fed a nutritionally sound diet.

Final points . . .
Transitioning heifers from high-forage diets to low-forage, limit-fed diets requires incremental steps to allow adequate rumen adaptation. Research at Penn State has focused on limit feeding high-concentrate diets to learn about limit-feeding systems; however, feeding higher-concentrate diets is a major nutritional and management shift from traditional heifer diets.

An appropriate starting point is limiting intake of a diet containing half forage and half concentrate. This diet offers some of the advantages of limit feeding a high-concentrate diet and will boost feed efficiency compared to a traditional high-NDF, low-energy diet. A 50 percent forage diet also is quite common on a dairy farm, as it is close to a lactating cow ration and is easily workable for heifers.

Limit feeding should be discontinued and heifers adapted to normal prefreshening diets 30 to 45 days before calving. This strategy has produced no adverse effects on calf birth weight, dystocia, metabolic problems, early lactation intakes, or first-lactation milk production in research. Changes in rumen and gut volume have been shown to occur rapidly and do not limit dry matter intake after calving. For more information about this research and example diets, visit: http://das.psu.edu/dairy/dairy-nutrition.

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