title: In vitro digestibility of individual amino acids in rumen-undegraded protein: the modified three-step procedure and the immobilized digestive enzyme assay.
abstract: Three soybean meal, 3 SoyPlus (West Central Cooperative, Ralston, IA), 5 distillers dried grains with solubles, and 5 fish meal samples were used to evaluate the modified 3-step in vitro procedure (TSP) and the in vitro immobilized digestive enzyme assay (IDEA; Novus International Inc., St. Louis, MO) for estimating digestibility of AA in rumen-undegraded protein (RUP-AA). In a previous experiment, each sample was ruminally incubated in situ for 16 h, and in vivo digestibility of AA in the intact samples and in the rumen-undegraded residues (RUR) was obtained for all samples using the precision-fed cecectomized rooster assay. For the modified TSP, 5 g of RUR was weighed into polyester bags, which were then heat-sealed and placed into Daisy(II) incubator bottles. Samples were incubated in a pepsin/HCl solution followed by incubation in a pancreatin solution. After this incubation, residues remaining in the bags were analyzed for AA, and digestibility of RUP-AA was calculated based on disappearance from the bags. In vitro RUP-AA digestibility estimates obtained with this procedure were highly correlated to in vivo estimates. Corresponding intact feeds were also analyzed via the pepsin/pancreatin steps of the modified TSP. In vitro estimates of AA digestibility of the feeds were highly correlated to in vivo RUP-AA digestibility, which suggests that the feeds may not need to be ruminally incubated before determining RUP-AA digestibility in vitro. The RUR were also analyzed via the IDEA kits. The IDEA values of the RUR were good predictors of RUP-AA digestibility in soybean meal, SoyPlus, and distillers dried grains with solubles, but the IDEA values were not as good predictors of RUP-AA digestibility in fish meal. However, the IDEA values of intact feed samples were also determined and were highly correlated to in vivo RUP-AA digestibility for all feed types, suggesting that the IDEA value of intact feeds may be a better predictor of RUP-AA digestibility than the IDEA value of the RUR. In conclusion, the modified TSP and IDEA kits are good approaches for estimating RUP-AA digestibility in soybean meal products, distillers dried grains with solubles, and fish meal samples.
authors.affiliation: Department of Biological Sciences, University of New Hampshire, Durham, NH 03824, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Boucher
authors.forename: S
authors.initials: S
authors.lastname: Calsamiglia
authors.forename: C M
authors.initials: CM
authors.lastname: Parsons
authors.forename: M D
authors.initials: MD
authors.lastname: Stern
authors.forename: M Ruiz
authors.initials: MR
authors.lastname: Moreno
authors.forename: M
authors.initials: M
authors.lastname: Vázquez-Añón
authors.forename: C G
authors.initials: CG
authors.lastname: Schwab
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D000821:Animal Feed / Q000032:analysis*; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D004044:Dietary Proteins / Q000032:analysis; D004063:Digestion; D004800:Enzymes, Immobilized / Q000378:metabolism; D012417:Rumen / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D004800:Enzymes, Immobilized