| This research was conducted to investigate the effects of dietary protein levels on the mechanism of peptide release and the content of peptide amino acid in total amino acids (PAA/TAA) in Hu sheep. Peptide molecular weight was analyzed by LC/MS. And we analyzed different kinds of Peptide release and the dynamic changes of PAA/TAA in gastroenteric tract and blood. For this objective, three Hu sheep which were fitted with ruminal cannulae, duodenal cannulae, portal venous, jugular vein and carotid artery catheters were fed with four different diets at crude protein level of 8.4%(A), 11.2%(B),14.0%(C) and 16.8%(D) respectively. The results showed as follows:1. pH in the rumen increased in accordance with the increment of dietary protein levels. pH was 6.28,6.39,6.40,6.49 in four group respectively. pH in group D was higher than that in group A significantly (p<0.01). pH decreased after feeding, and reached the lowest point 4h after feeding. pH in duodenum was 2.15,2.22,2.26 and 2.35 respectively, pH in group D was higher than that in group A significantly (p<0.05).2. The concentration of NH3-N in the rumen also increased with the increase of dietary protein levels. NH3-N increased after feeding, and reached the highest point 4h after feeding. In the duodenum, NH3-N concentration was 7.37,8.60,8.63,11.26 mg/100mL respectively, group A was significantly different from C and D group (p<0.01), and lower than group B significantly (p<0.05). and group B was lower than group D significantly(p<0.05).3. The content of ruminal MCP also increased with the increase of ration protein levels. MCP was 4.18,4.98,5.14and 5.24mgN/100mL respectively, group A was lower than that of other groups significantly(p<0.05). 4. The concentration of FAA and peptides in the rumen increased with the increase of dietary protein levels, group A was the lowest, and group C was the highest, group C was higher than that in group A significantly (p<0.05). Concentration of PAA was 10.52,10.70,14.04 and 14.96mg/100mL respectively, group D was significantly different from group A and B (p<0.01), and higher than group C significantly(p<0.05) , and group C was higher than that in group A and B significantly (p<0.05). In duodenum, concentration of FAA in group A was the lowest. And group D was the highest. group D was higher than that in group A (p<0.05), and no significant difference between B and C groups. Concentration of PAA in all groups attained peak value at 4h. PAA in group D was the highest (14.28 mg/100mL), group A was the lowest, groups C and D were higher than that of groups A and B significantly (p<0.05).5. Concentration of FAA and PAA in mesenteric vein attained peak 4h after feeding, then started decline and increased with the increase of ration protein levels.6. The concentration of FAA in portal vein had similar change trend with that in mesenteric vein. All groups attained peak value after feeding for 4h, then started going down. Group D was the highest, and group D was higher than that in group A (p<0.05). The concentration of PAA in groups C and D was higher than that in group A significantly (p<0.05).7. For FAA in carotid artery,there was no significant difference in the four groups. Whereas the concentration of PAA increased with the increase of dietary protein levels. Concentration of PAA were 30.56,31.96,32.25,33.69mg/100mL respectively, group D was higher than that in group A significantly (p<0.05).8. Peptide amino acid in total amino acids changed little in blood, and was higher than that in gastroenteric tract. The range of PAA/TAA in portal and mesenteric vein was 70%~80%, compare to 60%~70% in artery and gastroenteric tract.9. The net flux of PAA both in PDV and MDV increased with the increase of dietary protein levels. There was significant difference among the four groups (P<0.01or P<0.05). Particularly, the net flux of PAA in PDV increased significantly(P<0.01).10. The concentration of PAA in portal vein had a significant correlation with that in rumen based on correlation analysis. MCP in Group C had a significant correlation with PAA in the rumen 11. The amounts and varieties of Peptides both in gastroenteric tract and in blood were different in response to different dietary protein levels. The molecular weight of peptide distributed between 100 and 500 and mostly obtained between 200 and 399. Dietary protein level has little influence on the distribution of peptide content in Hu sheep.
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