Abstract: This experiment was conducted to investigate the effects of tannic acid on digestive enzyme activity and digestibility of dry matter and crude protein of corn-soybean meal diet in the simulated gastric and small intestinal digestion for growing pigs, which will provide a reference for evaluating the biological effects of tannic acid. In the experiment 1, a single factor completely randomized arrangement was used to investigate the effects of 2 tannic acids without diet on digestive enzyme activities in simulated gastric and small intestinal fluid for pigs. Five treatments consisted of 0 mg tannic acid (the gastric fluid volume was 20 mL, the intestinal fluid volume was 22 mL);tannic acid 1,10 mg; tannic acid 1,20 mg; tannic acid 2,10 mg; tannic acid 2,20 mg. The activities of pepsin, amylase, trypsin and chymotrypsin were determined. The experiment 2 was to investigate the effects of tannic acid supplemention in corn-soybean meal diet on digestive enzyme activity in gastric and small intestinal simulated digestion phases and nutrient digestibility determined with the simulated digestion for growing pigs. Five treatments of dietary tannic acid concentration were 0 mg·(2 g)^-1; tannic acid 1, 10 mg·(2 g)^-1; tannic acid 1, 20 mg·(2 g)^-1; tannic acid 2, 10 mg·(2 g)^-1; tannic acid 2, 20 mg·(2 g)^-1, respectively. The activities of pepsin were measured at 0.5 and 4 h in the gastric digestion phase, and the activities of amylase, trypsin and chymotrypsin were measured at 0.5, 4, and 8 h in the small intestinal digestion phase. Simultaneously, the digestibility of dry matter and crude protein were determined for the diet. The results showed that:1) Without the diet, compared with the blank control group, the 2 tannic acids didn't significantly affect the activity of pepsin in the simulated gastric fluid(P>0.05); tannic acid 1 significantly reduced the activities of amylase, trypsin and chymotrypsin in the simulated intestinal fluid contrast to tannic acid 2 (P<0.05). 2) From 0.5 to 4 h of the simulated gastric digestion, except for the 10 mg·(2 g)^-1 supplementation level at 4 h, the activity of pepsin in simulated gastric fluid in the tannic acid 1 diet was significantly greater than that in the tannic acid 2 diet(P<0.05). Except for tannic acid 2 at 0.5 h, the pepsin activities in simulated gastric fluid in the 2 tannic acids added at 10 mg·(2 g)^-1 were significantly greater than that at 20 mg·(2 g)^-1(P<0.05). At 0.5 h of the simulated small intestinal digestion, except for the chymotrypsin activity at 20 mg·(2 g)^-1 supplementation level, the 2 levels of tannic acid 1 or 2 in the diet didn't significantly influence amylase activity in the digestive fluid(P>0.05), but both significantly reduced chymotrypsin activity(P<0.05). The trypsin activity of the digestive fluid in the tannic acid 1 was greater than that in the tannic acid 2(P<0.05). At 4 h of the simulated small intestinal digestion, except for the chymotrypsin activity at 20 mg·(2 g)^-1 supplementation level, the activities of amylase and chymotrypsin in digestive fluid was greater but the trypsin activity was lower in diet supplemented with tannic acid 1 than tannic acid 2(P<0.05). The supplement of tannic acids 1 and 2 reduced the activities of trypsin and chymotrypsin (P<0.05). At 8 h of the simulated small intestinal digestion, the concentration of tannic acid in diet affected the activity of amylase, but no significant difference was observed on the average activity of amylase between the treatments of tannic acid 1 and tannic acid 2(P>0.05). The supplement of tannic acids 1 and 2 reduced the activities of trypsin and chymotrypsin(P<0.05). 3) Campared with the control, the 2 tannic acids significantly reduced the digestibility of dietary crude protein at both levels (P<0.05). More reduction in digestibility of dietary crude protein was observed in tannic acid 2 than tannic acid 1 (P<0.05). In summary, inconsistent effect of tannic acid on digestive enzyme activities was presented in digestive fluid with or without diet, the tannic acid reduced the dietary crude protein digestibility maybe mainly related to the reduced activities of chymotrypsin in the digestive fluid and hydrolysis efficacy of digestive enzymes reduced by the formation of chelates between tannic acid and dietary components in the simulated digestion for growing pig.

Key words: growing pig, simulated digestion, tannic acid, digestive enzyme activity, nutrient digestibility