Rumen degradability and ileal digestibility of proteins and amino acids of feedstuffs for cows

Knowledge of the profile of amino acids of the rumen-undegradable protein can help in the formulation of diets to provide amino acids that complement microbial protein as well as supply amino acids, which are most limiting for milk production. Three non-lactating cows fitted with rumen cannulas were used to determine the effect of in situ rumen degradation on crude protein and amino acid profile of rumen-undegraded protein of feedstuffs. The obtained values of rumen degradability of crude protein with significant difference (P < 0.001) between feeds ranged from 20.3 to 76.3% (mean 62.0 +/- 17.9%) and values of total amino acids ranged from 30.9% in corn gluten meal to 83.8% in corn gluten feed (mean 67.5 +/- 16.4%). An in vitro modified 3-step method was used to determine intestinal digestibility. Intestinal digestibility of undegraded protein varied from 54.5 +/- 1.4% in raw soybean to 95.2 +/- 1.0% in corn gluten feed. The absorbable amino acid profile of rumen-undegraded protein for each feedstuff was compared with profiles of the original feedstuff and the rumen-exposed undegraded protein. Absorbable lysine (9.3 +/- 1.1 g/kg of crude protein) was higher in products of soybean and sunflower cake. Corn gluten feed and meal supplied more absorbable methionine (3.6 +/- 0.6 g/kg of crude protein). This study showed that the digestibility factor of crude protein and amino acid based on in situ and in vitro methods for thermal treatment of protein feeds can be used in models to optimize the amino acid nutrition of dairy cows and expand knowledge about rumen degradability and ileal digestibility of amino acids in feedstuffs.