| In this study, artificial small intestinal fluids were prepared with enzyme reagents based on the activities of digestiva enzymes, ion concentrations and pH value of the small intestinal juices in aged layers. A pepsin-artificial small intestinal fluid in vitro digestion method using bionic digestion system was established according to the difference between in vitro digestion and biological method.Experiment l: The study was conducted to investigate the effects of dietary protein source on the composition of intestinal fluid in layer-type cockerel, which would provided biological basis for simulating intestinal fluid in feedstuff evaluation using in vitro digestion. The 2×2 factorial completely randomized design was adapted. Twenty-four duodenal and 24 jejunal cannulated hyline brower layer-type cockerels with similar weight were selectd and divided into 2 groups of each type cannulated birds with 4 replicates of 3 cokerels. Duodenal or jejunal digesta samples were collected for 1 h every 4 h from 9:30 to 18:30 h on d 31, 33, and 35 of the experiment. The intestinal fluid was made by centrifuging digsta samples at 4℃. The results showed that there were higher trypsin activity and CL- concentration but lower K+ concentration of jejunal fluid, and higher lipase activity but lower Mg2+ concentration of duodenal fluid in cockerel fed corn soybean meal diet than that of birds fed corn-soybean-cottonseed meal diet (P<0.05). The composition of intestinal fluid from different position in the small intestine showed the amylase and trypsin activity, Na+ and Mg2+ concentration, pH were lower, but lipase activity, K+ and CL- concentration were higher in duodenal fluid than that in jejunal fluid (P<0.05). There were lower amylase and trypsin activites, but higher lipase activity in duodenal fluid than that in jejunal fluid ( P<0.05). In conclusion, there were significant effects of dietary crude protein source on the digestive enzyme and ion concentration of intestinal fluid and significant difference in the composition of intestinal fluid from different position in the small intestine in layer-type cockerel.Experiment 2: In the second part the suitable hydrolyzation time at each simulative digestion stage in bionic digestion system was investigated to provide a reference for designing the process of in vitro digestion in layer feedstuff. The single factorial randomized design was adapted to study the gastric and intestinal simulative digestion time. The results showed that, in gastric simulative digestion stage, there was not significant difference in digestibility of dry matter and digestive energy of corn-soybean meal diet and corn-soybean-cottonseed meal diet digested for 4 h, 5 h and 6 h(P>0.05), which was significantly higher than these measured at 1 h, 2 h and 3 h ( P<0.05 ). In intestinal simulative digestion stage, the difference of 12 h, 15 h and 18 h dry matter digestibility of corn-soybean meal diet was not significant (P>0.05) , but the 12 h digestive energy was significantly lower than that of 15 h and 18 h ( P>0.05 ). The dry matter digestibility and digestive energy of corn-soybean-cottonseed diet were significantly increased from 12 h to 15 h simulative digestion ( P<0.05 ), but no longer increased after digested from 15 h to 18 h. In conclusion, the optimum time of gastric and intestinal simulative digestion was 4h and 15h, respectively.Experiment 3: The third part was conducted to compare the precision of metabolizable energy using digegtion bionic method with the bioligical method in 10 cottonseed meal samples and 10 soybean meal . Results showed that there was no significantly difference (P>0.05) between the average DEBM and TME of 17 samples. However the average DEBM of the rest 3 samples was significantly lower (P<0.05) compared with the TME. In conclusion, it was acceptable for DEBM to estimate TME in layer feedstuff.The precision and distinguish ability of DEBM were better than TME. |
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