Study On Determination Of The Digestibility Of Amino Acid In Grain And By-products Based On Simulating The Protein Digestion Process In Roosters

The objective of this study was to investigate the passage time of digesta in digestive tract of yellow-feathered roosters and in vitro digestion time to establish an in vitro digestion method for predicting digestibility of amino acid in grain and by-products based on simulating in vivo digestion process in roosters,which will provide a reference for the rapid evaluation of the nutritional value of protein.Experiment 1 was to study the effects of cottonseed meal and soybean oil levels on passage time and digestibility of amino acids in yellower-feathered rooster.Four diets were used in a 2×2 factorial completely randomized design with 2 levels of cottonseed meal(CM)(20% or 40%)and 2 levels of soybean oil(SO)(0% or 10%).Eighty-five Chinese yellow-feathered roosters(BW = 2.61 ± 0.08 kg;26wk-old)were individually weighed and allotted to experimental diets.The time-relative cumulation of excreta,mean retention time(MRT)of digesta in the digestive tract,and standardized ileal digestibility of amino acids in cottonseed meal were measured.The results showed that: 1)Increasing dietary CM levels reduced the time for 50% relative cumulation of dry excreta(P<0.05).Adding 10% SO in diets tended to increase the time for 50% relative cumulation of dry excreta(0.05<P<0.10).2)Increasing dietary CM levels reduced the MRT in the jejunum and gizzard plus small intestine(P<0.05),and SO levels had no effect on the MRT of digesta in each digestive tract.3)Increasing the dietary CM levels had a tendency to reduce the standardized ileal digestibility(SID)of lysine,and supplemented with 10%SO in diets tended to reduce the SID of Met(0.05<P <0.10).Experiment 2 was to study the effect of simulated digestion time on digestibility of amino acids.A single factor completely randomized design was adopted with the 8 h or 10 h simulated digestion time for the gastric-small intestine according to digesta passage time in experiment 1.The total digestion time of 8h includes 2 h of gastric digestion,3 h of anterior small intestine digestion,and 3 h of posterior small intestine digestion.The total digestion time of 10 h includes 2 h of gastric digestion,4 h of anterior small intestine digestion,and 4 h of posterior small intestine digestion.Eleven experimental diets or ingredients were used to evaluate the effect of simulated digestion time on digestibility of amino acids with 5 replicates per treatment,and 1 digestive tube for each replicate.The results showed that: 1)Increasing the simulated digestion time increased the digestibility of Cys in diet 1 and diet 3 of experiment 1(P<0.05),but had no effect on the digestibility of other amino acids in diets 1 to 4 of experiment 1.2)Compared with the 8 h digestion time,the 10 h digestion time increased the digestibility of amino acids in casein,corn gluten meal,cottonseed meal,rapeseed meal,corn and soybean meal(P<0.05).3)Simulated digestion time had no effect on the digestibility of any amino acids in corn-soybean meal diet.Experiment 3 was to study the correlation between in vivo method and simulated digestion system for determining the digestibility of amino acids in cereals and by-products.A single factor completely randomized design was used to determine the digestibility of amino acids in 15 cereals and by-products with the in vivo method and simulated digestion system.Each feed ingredient was determined for 4replicates with 3 roosters per replicate for in vivo method.There were 5 replicates of each feed ingredients with 1 digestive tube per replicate for simulated digestion.Excluding corn germ cake and corn DDGS,the correlation of the digestibility of amino acids between in vivo method and simulated digestion was analyzed for the remaining 13 ingredients.The results showed that the simulated digestion method can well predict the digestibility of amino acids except for Thr,His,Arg,Gly and Cys.The correlation coefficient of these amino acids was in the range of 0.71 to 0.89,especially for the Ile,Leu,Phe,Glu and Ala with correlation coefficient over 0.80.In conclusion,a significant correlation between the simulated digestion method and in vivo method was observed on digestibility of most amino acids in grains and by-products,and the digestibility of amino acids determined with these two methods were relatively close.