| This experiment was conducted to investigate the variation of digestive enzyme activities in the simulated digestion with digestion time,the contribution of main digestive enzymes in the simulated digestion of small intestine to the digestion of protein,the effect of clearance process in the simulated digestion on crude protein digestibility of cereal grains and the difference and correlation of amino acid digestibility of cereal grains determined with simulated digestion and in vivo digestion,which will provide a reference to develop the simulated digestion method for determining protein biological value of cereal grains for growing pig.The EXP.1 was conducted to investigate the variation of digestive enzyme activities during the stages of simulated gastric and small intestinal digestion and after supplementation digestive enzymes for pigs.In trial 1,a single factor completely randomized design was used to investigate the variation of digestive enzyme activity depending on digestion time in the simulated digestion for corn,soybean meal,wheat bran and corn-soybean meal diet.In trial 2,the digestive enzymes were supplemented at 4 h of small intestine phase and the variation of digestive enzyme activities after supplemental enzyme.The results showed as follows: 1)When the simulated gastric fluid was mixed with four substrates,the specific activity of pepsin in the digestive fluid was rapidly reduced.However,from 1 to 4 h of the simulated digestion,the specific and total activities of pepsin were increased with the quadratic curve(P<0.05).The final values were from 78.0 to 96.1% relative to initial specific activity or from 87.2 to 102.7% relative to initial total activity of simulated gastric fluid,respectively.In the small intestine digestion phase,different extent of reduction of enzyme activities was observed in simulated digestive fluid(P<0.05).The quadratic or non-linear curve variation of amylase and chymotrypsin activity in digestive fluid was observed on different substrates(P<0.05).The quadratic reduction was observed on trypsin activity in digestive fluid(P<0.05).The greatest reduction of activity was observed in trypsin.2)After the digestive enzymes were supplemented in simulated small intestinal digestion,the specific activities of amylase,trypsin and chymotrypsin in the digestive fluid could be recovered to the initial value,but they still decreased with the digestion time(P<0.05).The trypsin activity still decreased rapidly.The EXP.2 was conducted to investigate the contribution of composition and activity of main digestive enzymes in simulated digestion of small intestine to the digestion of nutrients in feed for pig.Five treatments consisted of gastric simulated digestion,gastric following amylase for small intestinal simulated digestion,gastric following amylase and chymotrypsin for intestinal simulated digestion,gastric following amylase,chymotrypsin and trypsin for intestinal simulated digestion,gastric following amylase,chymotrypsin,trypsin and supplemented digestive enzymes at 4 h for intestinal simulated digestion were arranged in a single factor completely randomized design.The differences in digestibilities of dry matter,crude protein or energy and the contribution of each digestive enzyme to nutrient digestibility were investigated among various treatment conditions for each of corn,soybean meal,wheat bran and corn-soybean meal diet.The results showed as follows: 1)Amylase and chymotrypsin in simulated intestinal fluid could significantly increase the digestibilities of dry matter,crude protein and energy in four substrates digested by simulated gastric fluid(P<0.05).Trypsin could further increase the digestibilities of dry matter,crude protein and energy in soybean meal and wheat bran digested by simulated gastric fluid(P<0.05).The supplement of 3 digestive enzymes at 4 h of intestinal digestion could increase the digestibilities of the crude protein digestibilities of wheat bran,and the digestibility of dry matter,crude protein and energy in corn-soybean meal(P<0.05).2)The contribution of digestive enzymes in the small intestinal fluid to the digestibilities of feed nutrients varied depending on the feed substrate.Amylase and chymotrypsin had relative greater contribution to the digestibilities of energy and crude protein contrast to trypsin and supplemented digestive enzymes.However,trypsin and supplemented digestive enzymes also significantly increased the nutrient digestibilities(P<0.05).The EXP.3 was conducted to investigate the effect of clearance process in the simulated digestion on the crude protein digestibility of cereal grains.A single factor completely randomized design was arranged for 3 treatments consisted of the crude protein digestibility determined with the simulated digestion-12 h clearance,the crude protein digestibility determined with the simulated digestion-24 h clearance and the standard ileal protein digestibility of the in vivo method.There were 5 replicates of 1 digestion tube in each for simulated digestion and 6 replicates of 5 pigs in each for in vivo bioassay.Fourteen cereal grains were determined for crude protein digestibility with each treatment.The results showed as follows: in 14 cereal grains excluding 2 rices,the difference between the simulated digestion-24 h clearance and the in vivo method for the determination of crude protein digestibility was 0.46 to 10.82%,and the correlation coefficient was r=0.9186.Whereas the difference between the simulated digestion-12 h clearance and the in vivo method for the determination of crude protein digestibility was 0.77 to 6.84%,and the correlation coefficient was r=0.9519.Consideration of the similar values and correlation between simulated digestion and in vivo bioassay,the simulated digestion-12 h clearance was more suitable to determine the digestibility of crude protein in feed.The EXP.4 was conducted to investigate the correlation between in vivo and the simulated digestion for determining the digestible amino acid content and amino acid digestibility of cereal grains.A single factor completely randomized design was adopted to determine the amino acid digestibility of 14 cereal grains with the simulated digestion and in vivo method.Each feed sample was determined for 5 replicates of 1 digestion tube per replicate in simulated digestion and 6 replicates of 5 pigs per replicate in in vivo bioassay.Excluding 2 rice grains,the correlation was analyzed between simulated digestion and in vivo method for the digestible amino acid content and amino acid digestibility of 12 cereal grains.The results showed that the simulated digestion method can well predict the standard ileal digestible amino acid content of 16 amino acids with the correlation coefficients over 0.95;The simulated digestion method can predict the SID of 15 amino acids except Arg.The correlation coefficients between simulated digestion method and in vivo bioassay ranged from 0.5779 to 0.9387.Especially,the correlation coefficients over 0.82 were observed for the dispensable AA including Lys,Leu,Ile and Phe and the dispensable AA including Asp,Ser,Glu and Ala. |
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