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Evaluation of in vitro dry matter digestibility (IVDMD) of high fiber feed ingredients for monogastrics
The IVDMD of feed ingredients can be used to rapidly estimate the amount of energy and nutrients that will disappear in vivo during digestion in the stomach and small intestine, and during large intestinal fermentation in monogastric animals. Digestible DM variability after hydrolysis with pepsin and pancreatin has been published for cereal grains and oilseed meals, but not for high fiber feed ingredients. Therefore, the objective of this experiment was to measure IVDMD of multiple sources of distillers dried grains with solubles (DDGS, n = 16), soybean hulls (SBH, n = 16), and wheat straw (WS, n = 16) using a modified pepsin and pancreatin hydrolysis procedure. Gastric hydrolysis was set for 2 h, at pH 2.0 in a pepsin solution (400 mg/mL). Small intestinal hydrolysis was set for 4 h, at pH 6.8 in a pancreatin solution (400 mg/mL). After hydrolysis, residues were filtered into nylon bags (pore size 50 μm) and sequentially washed twice with 95% ethanol and 99.5% acetone. The IVDMD was calculated as disappearance of DM from initial sample weight. All samples of each source were analyzed in 6 batches, and the mean, SD, and CV were calculated among replicates within each ingredient source. Repeatability of measurements was considered acceptable when CV was < 3% for DDGS and < 4% for SBH and WS. Data were analyzed using the GLM procedure of SAS with sample source as a fixed effect. The IVDMD in DDGS (55.6%) was greater (P < 0.01) than SBH (20.0%) and WS (14.6%), and IVDMD in SBH was also greater (P < 0.01) than WS. There were also differences in IVDMD among sources of each ingredient. The IVDMD varied among DDGS sources (P < 0.01) from 45.6 to 61.9%, among SBH sources (P < 0.01) from 17.2 to 23.2%, and among WS sources (P < 0.01) from 11.6 to 18.2%. In conclusion, the extent and variability of IVDMD among DDGS sources is greater than for SBH and WS, and differences in IVDMD observed among sources of each ingredient were large enough to impact the concentration of digestible energy and nutrients in the small intestine of monogastric animals. Further fermentation of hydrolyzed residues will allow us to measure the concentration of fermentable nutrients.
Keywords: high fiber ingredients, in vitro dry matter digestibility, monogastrics