| The study was on the rule of variation of digestive gut (gizzard, proventriculus and small intestine) and juice development of adult layers to set up an in vitro digestion method for nutritional value of conventional feedstuff.Experiment 1 Study on the Gastrointestinal Parameters of adult layersIn this experiment,Digestion parameters of adult layers in different age were determined to set up the gastrointestinal parameters model.1440 22-weeks layers were randmly assigned to 4 groups with 8 repeats 45 each and fed corn-soybean meal diet. Layers at 24, 25, 34, 44, 54 weeks old were killed to get the chyme in crop, proventriculus and gizzard, duodenum, jejunum and ileum. Moisture, pH and digestive enzyme activities were measured respectively. The length of duodeum, jejunum and ilenum were measured too.The result showed that chyme pH in gizzard and proventriculus increased gradually with age in 24~54 weeks and kept stable in jejunum. Moisture of chyme in jejunum, gizzard and proventriculus kept stable with age. Moisture in jejunum obviously higher than that in gizzard and proventriculus. The small intestine has developed steady and no changes with age. The content of TBA increased gradually with age. Between 24 and 44 weeks the content of TBA was higher and stable, but droped rapidly after 44 weeks.Pepsinum activities in adult layers decreased with age but kept stable between 24 to 34 weeks and droped rapidly after 44 weeks. Lipase, trypsin and chymase activities kept stable in 24 to 44 weeks. Chymase and amylase activities droped rapidly after 44 weeks.Experiment 2 Digestive and metabolic trial for adult layers in vivoIn this experiment,240 35- weeks healthy layers were randmly assigned to 3 groups with 2 repeats 20 each which were fed corn-soybean meal diet with chromiumoxide as indicator. It lasted 4 weeks. Feaces were collected for three days and dried at 65oC. The digestibility of crude protein, energy and amino acid of adult layers were determined. The result showed that the digestibility of crude protein, energy and amino acid of adult layers kept higher and stable relatively.Experiment 3 Establish of digestion method in vitro for layerIn vitro digestion method includes four parts: establishment of digestive parameters, design of bioreactor, establishment of digestive steps and optimization of in vitro digestion condition.Establishment of digestive parameters:In this stage, pH, moisture, digestive enzymes level and chyme retention time in crop, proventriculus, gizzard and small intestine were determined respectively according to the results of experiment 1. Commercial digestive enzymes(pepsin, pancreatin, trypsin, amylase and lipase) were used to imitate that of adult layers gastric-intestinal tract respectively.Design of bioreactor:according to the principle of bionics, bioreactor of layer gastric-intestinal tract has the following several parts: digestion device, constant temperature control device, flow speed control device and digestive juice receivers.Establishment of digestive steps: digestive steps of layer were the crop digestion phase, stomach digestion phase and intestine digestion phase.Optimization of in vitro digestion condition: test showed that the optimal feed size was 60 mesh and dialysate flow speed was 1.5ml/min.Experiment 4 Test for in vitro digestive methodAccording to the result of Experiment 3, the digestibility of amino acid of the feed were measured to test the feasibility of the method of in vitro digestion. Results showed that digestibility of total amino acid has not significant difference between in vitro and in vivo. The digestibility of aspartic acid, glutamate, arginine, valine, leucine, phenylalanine and tyrosine had obvious differences between in vitro and in vivo.
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