|Akins, Matthew - University Of Wisconsin|
Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: 3/4/2019
Publication Date: 3/15/2019
Citation: Coblentz, W.K., Akins, M.S. 2019. A look at fiber, energy, and intake relationships for pregnant dairy heifers. Popular Publication. pp 14-15.
Technical Abstract: A common problem for producers raising dairy heifers is the potential for excessive weight gains that results in over-conditioning. This is especially problematic for pregnant dairy heifers that have lower energy requirements than younger heifers, and may contribute to subsequent metabolic problems and depressed first-lactation milk yields. In general, there are two strategies to combat this problem, which include: 1) dilution of diets with low-energy forages; or 2) limit-feeding (not discussed). Over the last decade, we have conducted 5 pen-based studies at the University of Wisconsin Marshfield Agricultural Research Station, mostly evaluating techniques for using diluting agents, such as straw, to reduce caloric intake by pregnant heifers. As such, a summary of these experiments (14 diets) offers some clear illustrations of relationships between fiber, energy, and ad-libitum intake by heifers. Although determination of energy (TDN) is complex, involving many inputs, it is clear that a primary driver for energy density in these diets was structural plant fiber (NDF), which explained about 77% of the variability in energy. For these diets, including diluting (high-NDF) agents, such as straw, reduced the energy density of the diet, and is one (partial) mechanism for restricting caloric intake by heifers. Increasing the NDF concentration within the diet provides another partial mechanism for reducing caloric intake by heifers because past work has suggested that intake may be capped by gut fill when heifers consume 1.0% of bodyweight as NDF. For this data set, maximum NDF intake was 0.99% of BW for diets ranging from 48.5 to 54.0% NDF, thereby corroborating past work. Furthermore, this resulted in a about a 0.25-percentage unit reduction in dry matter intake when diets ranged from 39 to 53% NDF. Dilution of alfalfa/corn silage diets with low-energy forages works to restrict caloric intake by two mechanisms: 1) reducing the energy density of the diet; and 2) reducing DM intake.