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Dollars in your pocket: Dairy heifer nutrition

Gustavo Lascano for Progressive Dairyman Published on 18 April 2017

Feeding practices affect the performance of the dairy heifer and the time necessary for the animal to be bred and to attain an optimal size, age and mammary development. It is extremely important that dairy producers realize the impact feeding practices and type of diet will have on the replacement animals, which are usually fed low-quality ingredients in order to reduce rearing costs.

Studies reporting the impact of using precision feeding strategies for dairy heifers have addressed the manipulation of different forage-to-concentrate proportions in the diet, dietary fiber, non-structural carbohydrates, protein levels and fractions, and the interaction among them. In this article, we will review some of these results.

While practices of managing lactating dairy cattle occupy the greatest share of time, effort and costs associated with dairy farming, the total costs of raising dairy heifers are the second-largest contributor to the annual operating expenses of most dairy farms at about 20 percent of total expenses.

Feed costs represent over 60 percent of these costs, resulting in a total contribution of dairy heifer feed toward operating expenses of about 12 percent. This large contribution toward operating expenses indicates that an opportunity exists to reduce whole-farm expenses by reducing the expenditures of raising dairy heifers through improving nutritional management practices.

One method that would result in accomplishing a substantial economic reduction in costs is to reduce feed intake and precisely meet animals’ requirement for growth, where nutrients supplied to the animal meet requirements for an optimal average daily gain (ADG), achieving the desired age at first calving of 22 to 24 months.

Precision-feeding nutrients in the right combination has been used to replace the typical ad libitum feeding approach, reducing unused nutrients and waste, where feed efficiency has been maximized.

Results of a series of experiments have demonstrated the feasibility of adapting this strategy to raise dairy heifers. An optimal pre-pubertal ADG of approximately 800 grams per day was defined as adequate to optimize milk production in Holsteins during first and second lactation in a study published in 2005.

This target ADG allowed researchers to start finding how to deliver nutrients in the most effective way. Increases on digestibility and feed efficiency were observed with the use of high-concentrate diets in comparison to control high- forage diets; these results observed a reduction of 10 to 40 percent in feed intake relative to ad libitum systems.

Yet no changes in growth, rumen fermentation and health of the animals were reported.

These effects on rumen fermentation can be explained due to the lower pool of readily available carbohydrates such as starch and sugars that, when offered ad libitum, typically result in low rumen pH leading to subclinical and clinical acidosis.

Controlling the intake results in similar net energy required for growth, but metabolic costs required to attain similar ADG are reduced, indicating there is a higher loss of energy in metabolic heat for high-forage diets, especially when they are low-quality.

This increase in feed efficiency due to the reduction in feed intake and energy expenditure has also been accompanied by similar milk production when different forage-to-concentrate proportions have been used to attain equal ADG rates during the pre-pubertal, post-pubertal and gravid period.

One of the key points that often results in producers not adopting this feeding strategy is the growth monitoring required to successfully undertake this system.

In general, a monthly weighing and structural measurement is recommended to ensure that the ADG is being attained.

Typically, as animals are subjected to limited amounts of intake and if nutrients are provided in the right proportions, a continuous increase in efficiency has been observed and, if not monitored, this can result in over-conditioned animals more prone to metabolic problems and to a reduction in milk production due to the accumulation of adipose tissue in the mammary gland.

This nutritional approach can be used with different sources of readily available carbohydrates or lower digestible ones. The use of starch or soluble fiber is a viable option when diets are formulated appropriately, but also more recalcitrant ones such as corn stover have yielded interesting results – specifically, the positive effect that fiber incorporation might have on protein utilization.

The use of direct-fed microbials such as live yeast products has resulted in higher digestibility coefficients when used strategically (i.e., high concentrate with high fermentation potential).

To understand these effects, it is important to highlight the shift in digestion kinetics that occurs when going from an ad libitum to a controlled intake nutritional program.

For example, high-concentrate diets need to be fed at a lower amount to reach the same targeted ADG that a lower-quality, higher-forage diet achieves (Table 1) and are retained in the rumen for longer periods of time.

Two diets

Two diets

This explains the increased digestibility consistently observed on experiments where reduction in feed intakes have been planned to provide specific amounts of nutrients precisely. On the other hand, opposite to what we commonly see in ad libitum higher-forage systems, more fibrous sources reduce rumen retention time, increase this passage rate and reduce nutrient utilization.

Recently, a closer look into protein level and degradability has been the focus of investigation. An optimal level of nitrogen intake for heifers fed either high- or low-concentrate diets was reported to be 1.67 grams of nitrogen per kilogram of metabolic bodyweight.

This amount has been tested in several studies with good results related to protein utilization. With this preamble, other experiments looking at rumen protein degradability and sources coming from true protein or non-protein nitrogen highlighted an opportunity to improve nitrogen utilization depending on the forage-to-concentrate proportions and the level of dietary fiber.

Together, these results suggest that the rumen-soluble and degradable protein fraction of the diet can be manipulated with different responses expected as the forage level of the diet changes. To a level, non-protein nitrogen can replace true protein, and the level of protein degradability can complement this enhanced utilization to maximize microbial protein synthesis and animal performance when dairy heifers are fed an optimal nitrogen intake.

Higher rumen-undegradable protein seemed to be necessary to complement low fermentation potential when additional fiber is added under these conditions.

The knowledge built from these results demonstrates an opportunity to adopt this strategy with positive effects on animal performance through the different phases of the rearing period of dairy heifers.  end mark

Gustavo Lascano is an assistant professor of ruminant nutrition from Clemson University. Email Gustavo Lascanoo.

 

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