Digestive enzyme activity in frozen jejunal digesta was determined by commercial kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). Briefly, the samples were homogenized after dilution with saline (1:9), followed by centrifuging at 2,000×g for 10 min, and the aliquots were stored at −80°C for assay of enzyme activities. Then trypsin, lipase, amylase, lactase, sucrase and maltase activities were determined using commercial kits combined with UV-VIS Spectrophotometer (UV1100, MAPADA, Shanghai, China) according to the manufacturer’s instructions. The pH values of digesta were measured with a pH meter (PHS-3C pH, Shanghai, China) on d 14 and d 42.