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

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Abstract
Ruminal degradability of N and dry matter measured via the nondegradable bag technique was compared with in vivo degradation and the effect of varying ration degradability and physical form was studied 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 N 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 N and dry matter. Increasing particle size also increased ruminal degradation within estimated degradabilities. Microbial N delivered to the duodenum was correlated with N degradation in the rumen. Efficiency of microbial production of N was correlated with ruminal degradation of dry matter. Equations were dveloped to describe to relationshps. The in situ bag technique yields data on individual feedstuffs that can be used to formulate diets with defined ruminal degradability of N.