Ruminal and intestinal amino acid digestion of distiller's grain vary with grain source and milling process

Abstract

A study was conducted to evaluate the in situ ruminal degradability of crude protein (CP), amino acid (AA) profiles of ruminal undegradable protein (RUP), and in vitro intestinal digestibility of AA for dried distillers grains with solubles (DDGS) as affected by grain source (corn vs. wheat) and milling process (conventional vs. fractional). The feeds tested included wheat, wheat DDGS (WDDGS), corn, corn DDGS (CDDGS) and corn fractional DDGS (FDDGS). The feeds were evaluated in three ruminally cannulated beef heifers fed a diet containing 600g/kg barley silage and 400g/kg barley-based concentrate (dry matter [DM] basis). Polyester bags containing 5g of ground feed (2-mm) were incubated in the rumen of each heifer for 0, 2, 4, 6, 12, 16, 24, and 48h. Ruminal microbes were labeled using 15N to correct the bacterial contamination. The model y=a+b(1−e−c(t−lag)) was fitted to determine degradation kinetics of DM and protein. Effective degradability (ED) was determined as: a+[bc/(c+k)], where k was assumed to be 0.06/h. In vitro intestinal digestibility of the RUP and AA were determined on the residue after 16h of ruminal incubation using a modified 3-step method. The CP, neutral detergent fiber, acid detergent fiber, ether extract, and mineral contents of DDGS varied (P<0.01) with grain and milling process. Amino acid profiles of DDGS were different (P<0.05) from those of the original grain. Ruminal degradation of CP was lower (P<0.01) in DDGS than in the original grain, and lower (P<0.01) in FDDGS than in CDDGS, with no difference between WDDGS and CDDGS. However, ruminal degradation of essential AA (EAA) was higher (P<0.05) for WDDGS than for CDDGS, and it was lowest (P<0.01) for FDDGS. The AA profiles of RUP were different (P<0.05) between DDGS and the original grain as well as between DDGS types. Intestinal digestibility widely varied among individual AA and among feeds. The intestinal digestibility of total AA and EAA was not different between WDDGS and CDDGS, but it was lower (P<0.05) for FDDGS than for CDDGS. Estimated intestinal absorbable total AA and EAA were highest (P<0.05) for FDDGS, intermediate (P<0.05) for CDDGS, and lowest (P<0.05) for WDDGS. The results suggest that the AA availability of DDGS varies with the grain source used to produce ethanol and with the milling process prior to ethanol fermentation. Although FDDGS is a good RUP source, its CP digestibility coefficient in the total digestive tract of cattle is lower (P<0.05) than that of WDDGS and CDDGS.