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1 Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802
Dairy cattle require fibrous feedstuffs in the diet. However, defining the fiber requirements requires knowledge of many interacting components within the diet as well as how the feed is allocated and processed. To meet the demands of high producing dairy cows for energy, diets consist of large quantities of concentrates and high quality forages containing relatively low amounts of fiber. However, to maintain normal rumen function and milk fat percentage, a large portion of the fiber needs to come from forage. Current National Research Council recommendations are a minimum of 25 to 28% dietary neutral detergent fiber, 75% of which is supplied from forage. Chemical measures of fiber alone are not adequate for ration balancing; fiber varies in its effectiveness at stimulating chewing. This variation is greater when feeds contain high amounts of by-products in place of forages. The effectiveness in stimulation of chewing of fiber is variable as the particle size and retention times of indigestible and digestible fiber vary. Currently, little information exists about the fiber requirements of the cow from immediately postcalving until peak lactation. Early lactation cows are clearly more limited by physical fill than are cows in mid and late lactation. Rations based on nonforage fiber sources (>45% neutral detergent fiber on a dry matter basis) are being evaluated for early lactation cows. Information is needed to determine the variation in the amount of fermentation acids produced, chewing activity, and amount of saliva secreted as these all contribute to the physical effectiveness of fiber.
Key Words: neutral detergent fiber • fiber digestibility • nonforage fiber
Submitted on August 21, 1997
Accepted on January 26, 1998
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