Background: Microbial corrected in situ estimates of the ruminal undegraded fraction (RU) and intestinal effective digestibility (IED) of amino acids (AA), except tryptophan, of rye, wheat and corn grains, wheat bran, wheat and barley distilled dried grains and corn gluten feed were measured on three rumen- and duodenum-cannulated wethers using (15)N-labelling techniques and considering ruminal rates of particle comminution and outflow.
Results: The lack of microbial correction led to overestimations of the intestinal digested fraction that rose with the increase in ruminal degradability. Thus these overestimations varied widely among feeds (from 4.3 to 32.1% for total analysed AA) and among AA. Digestion led to large changes in the AA supply that were greater in the rumen than in the intestine. The impact of these changes on the protein value is conditioned by the magnitude of the undegraded protein fraction.
Conclusion: Microbial contamination taking place in the rumen and changes in the AA supply with digestion should be considered to attain accurate estimates of AA digestion. Globally, digestion improved the AA supply in rye, wheat and wheat distilled dried grain and decreased it in corn and corn gluten feed by reducing the supply of valine and basic AA, especially lysine.
Keywords: amino acids; intestinal digestibility; microbial contamination; ruminal degradability; sheep.
© 2014 Society of Chemical Industry.