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Nitrogen Degradability and Microbial Protein Synthesis in Calves Fed Diets of Varying Degradability Defined by the Bag Technique

Department of Dairy Science, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061

ABSTRACT

We compared ruminal degradability of nitrogen and dry matter measured via the nondegradable bag technique with in vivo degradation and studied the effect of varying ration degradability and physical form on ruminal microbial synthesis of protein. Steers (250 kg) were fitted with ruminal and duodenal cannulae. Determinations were dependent on a dual-phase flow marker system. In vivo preduodenal degradation of nitrogen averaged 7.2% more than predicted by the in situ bag technique. Increasing degradability as defined by the bag technique corresponded to increased ruminal degradation of nitrogen and dry matter. Increasing particle size also increased ruminal degradation within estimated degradabilities. Microbial nitrogen delivered to the duodenum was correlated with nitrogen degradation in the rumen. Efficiency of microbial production of nitrogen was correlated with ruminal degradation of dry matter. Equations were developed to describe both relationships. The in situ bag technique yields data on individual feedstuffs that can be used to formulate diets with defined ruminal degradability of nitrogen.

¹ Department of Animal and Dairy Science, Auburn University, Auburn, AL.

² Agway Inc., Agway Farm Research Center, Rd. #2, Tully, NY.