Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: 4/24/2017
Publication Date: 4/24/2017
Citation: Coblentz, W.K., Akins, M.S. 2017. The importance of NDF in constructing diets for dairy. Popular Publication. April 2017.

Interpretive Summary:

Technical Abstract: The goal of management programs for dairy replacement heifers is to consistently rear heifers at a low economic and environmental cost without compromising their future performance as lactating cows. Generally, this can be accomplished with forage-based diets, but a key to success is understanding the role of neutral-detergent fiber (NDF) in regulating both the energy density, as well as the voluntary intake of diets consumed by dairy heifers. More than a decade ago, Pat Hoffman (then at University of Wisconsin) established that dairy heifers offered forage-based diets will routinely consume approximately 1% of their bodyweight daily in NDF. In reality, this marker is a powerful tool for regulating the growth performance of dairy heifers. Within this context, significant amounts of corn silage in the diets offered to bred heifers for ad-libitum intake potentially creates two compounding problems: i) the energy density of corn silage is too high, and must be diluted with other low-energy forages to avoid over-conditioning; and ii) the NDF concentration within the overall blended diet may become too low, resulting in too much energy intake before the 1% of bodyweight threshold for NDF is reached. It is important to emphasize that these problems are not an either-or proposition; rather, they have compounding effects on the potential for over-conditioning. These problems created by inadequate NDF within the diet can be addressed by dilution with low-energy forages, such as straw, corn fodder, or even perennial warm-season grasses. However, when these forages are included in the diet, they are often less desirable, and may be actively sorted by heifers. Current University of Wisconsin recommendations for including straw in blended (TMR) diets suggest that nearly 100% of feed offered should be consumed within a 24-hour period in order to limit the effects of sorting on heifer growth performance.