An in vitro method for the estimation of ileal crude protein and amino acids digestibility using the dialysis tubing for pig feedstuffs

A new in vitro method using the dialysis tubing for predicting the ileal apparent digestibility (IAD) of crude protein (CP) and amino acids (AA) was proposed for pig feedstuffs. Under the laboratory condition, the procedure of the in vitro dialysis tubing method was as follows: a 1.0 g sample of feedstuff was placed in a 100 ml Erlenmeyer flask, 10 ml hydrochloric acid (0.01 M, pH=20) pepsin solution (1.0 mg pepsin/ml HCl) was added, and the mixture was incubated for 4 h at 37°C. Then after neutralization with 0.2 M sodium hydroxide, this mixture was transferred into a prepared dialysis tubing with 40 ml phosphate buffered saline (PBS) solution (0.02 M NaHPO4, 0.02 M Na2HPO4, and pH=7.6) and 10 ml trypsin PBS solution (2.0 mg trypsin/ml PBS) was added. Then, the open side of the dialysis tubing was tied tightly with nylon threads so that the liquid could not leak out. Finally, the dialysis tubing was put into a 1000 ml coneflask which was sealed with parafilm containing 300 ml dialytic liquid (PBS solution). The flask was incubated for an additional 24 h at 37°C. During the incubation period, the digested CP or AA could infiltrate into the 300 ml PBS solution. After the two-stage incubation, the in vitro CP and AA digestibility was calculated on the basis of the original CP and AA contents of feedstuffs and the CP and AA contents of the dialyzed solution. Linear regression equations were obtained between in vitro digestibilities and IAD of CP and AA for four feedstuffs commonly used for growing pigs (0.96<r<0.99). The results show that it is possible to predict IAD of feedstuffs using the in vitro digestibility data for growing pigs. This method is accurate, rapid, reproducible and particularly suited for the evaluation of a large number of samples under laboratory condition.