Digestion kinetics of neutral detergent fiber and chemical composition within some selected by-product feedstuffs

Abstract

Nine by-product feedstuffs (BPF) obtained from three different sources were evaluated for nutrient composition, estimated nonstructural carbohydrate (NSC) and TDN content, and total extent and rate of digestion of DM and NDF. The nine BPF evaluated included: beet pulp (BP), rice bran (RB), almond hulls (AH), citrus pulp (CT), bakery waste (BW), wheat mill run (WMR), brewers' grains (BG), distillery grains (DG) and soy hulls (SH). Twenty-seven samples were evaluated and were a subset of a larger study reported previously. In sacco techniques were used to measure the amount of NDF and DM remaining in nylon bags after 0, 1, 2, 4, 8, 16, 24, 36, 48, and 72 h of incubation in the rumen of a rumen fistulated cow. Chemical analyses measured included ash, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and crude protein in the NDF (NDFCP) and ADF (ADFCP) fractions. Chemical composition differed among BPF source. This difference could be due to processing method or ingredients added to BPF during processing. The amount of CP associated with the NDF fraction varied among sources of each BPF. The amount of NDFCP also differed for each BPF. The NDFCP content of CT, 0.44%, was low compared with DG, 14.5%, which was high compared with the other BPF evaluated. Correcting for the fiber-bound protein increased the estimate of NSC slightly for most BPF, but the NSC content of DG was increased 88%. The results indicate a correction for NDFCP is necessary for an accurate estimation of NSC in BPF. Within a given BPF, the extent and rate of digestion of NDF were different for each source. The TDN content of each sample was calculated using the rate of in sacco NDF digestion for each BPF at three theoretical rates of passage from the rumen. By-product feedstuffs containing a high proportion of NDFCP and a low rate of NDF digestion had the greatest decrease in TDN content as passage rate increased.