The ruminal degradation of dry matter, nitrogen and amino acids in wheat-based distillers' dried grains in sacco

Abstract

The ruminal degradability of dry matter (DM), nitrogen (N) and individual amino acids in distillers' dried grains (DDG) with solubles, differing in concentration of acid detergent insoluble nitrogen (ADIN) and the type of grain from which the DDG was prepared, were determined in sacco. The three groups of DDG were prepared with wheat grain and maize grain as fermentative substrates: (1) DG1, 70% wheat, 30% maize; (2) DG2, 75% wheat, 25% maize; (3) DG3, 100% wheat. ADIN was 16.7%, 8.9% and 9.7% of the total N in DG1, DG2 and DG3, respectively. The soluble and potentially degradable fractions, as well as the rates of degradation and lag times for digestion of DM, N and individual amino acids were determined. Effective degradability values were estimated at rumen particulate outflow rates ( k) of 0.08, 0.05 and 0.02 h −1. A high ADIN concentration in DG1 compared with DG2 was responsible for the lower ( P < 0.01) effective degradability for N and amino acids. Except for lysine, these lower values were due to a smaller ( P < 0.10) soluble fraction and a slower ( P < 0.01) rate of degradation of a larger ( P < 0.10) potentially degradable fraction. Only for lysine was the sum of soluble and potentially degradable fractions markedly less than 100%, with that sum smaller for DG1 than for DG2. A DDG prepared from 100% wheat, DG3, had a higher ( P < 0.05) effective degradability for N and some amino acids than a DDG prepared from a blend of maize and wheat, DG2; these differences were not as large as those due to a difference in concentration of ADIN. Since the sum of soluble and potentially degradable fractions for DM was approximately 90%, a limit to the degradability of DM was indicated. A difference in ADIN concentration, DG1 versus DG2, resulted in a 12% higher estimated escape of amino acids, other than lysine, from ruminal degradation at the rumen outflow rate of 0.05 h −1; the concentration of lysine in DG1 was 11% lower than that in DG2. A DDG with a higher concentration of ADIN had a lower ruminal degradability and a higher weight of N and amino acids, other than lysine in the DM that escaped ruminal degradation.