Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2007
Publication Date: July 8, 2007
Citation: Hall, M. 2007. Nutrient synchrony: sound in theory, elusive in practice. Journal of Animal Science Supplement. 85:124. Technical Abstract: The concept of improving animal performance through synchronizing ruminal availability of nutrients has been with us for at least 3 decades. Though theoretically appealing, research and field results have not supported this approach to diet formulation. Why? Essential to successful ruminal synchrony is the ability to predict available amounts and fates of diverse substrates. The substrates come from varied sources; their efficiencies of use and yields of products are affected by inherent properties, interactions, transformations, and passage. Substrate quality and availability is affected only in part by diet: for example, NPN, true protein, and peptides are contributed by diet and intraruminal recycling, with additional endogenous NPN contributions by the cow. Conversion of the ruminally degraded N sources to AA available to the cow depends greatly upon availability of fermentable carbohydrates and other nutrients that support microbial growth. However, changes in factors that alter rate or extent of substrate fermentation such as rate of passage or ruminal pH can alter nutrient yield from the rumen, and must be accounted for for synchrony to work. Yield of microbial protein from carbohydrate can be altered by type of N source available, but these may be available from intraruminal recycling and diet. Conversion of some carbohydrates such as sucrose and fructan to stored microbial alpha-glucan alters the prediction of carbohydrate available in the rumen. Our ability to estimate ruminally available substrate is also challenged by normal variation in feed composition and imprecision in component and digestibility analyses. To have any effect on performance, ruminal synchronization of nutrients needs to be in concert with specific nutrient demands of the animal. "Synchrony" implies a greater deliberate precision than may be currently possible to effect. Perhaps we should consider balance: Within the rumen and cow, can we generate conditions so that needed substrates or nutrients are concurrently available or accessible from endogenous resources to enhance productivity and efficiency? This approach brings a broader view than focusing on the rumen and feed we offer to the cow.