| In this study,chitosan and weaned piglets were used as experimental subjects.The chitosan was firstly expanded,and the physicochemical properties of chitosan before and after expanded were characterized.Secondly,the bactericidal activity of expanded chitosan on pathogenic Escherichia coli and Staphylococcus aureus were examined in vitro experiments respectively,and the effects of expanded chitosan on growth index,intestinal morphology,nutrient digestibility and digestive enzyme activity of weaned piglets were investigated by in vivo experiments.The experiment selected 72 pairs of 28-day-old Duroc × Landrace × Big ternary hybridization weaned piglets with same parity,body condition,where are randomly divided into 4 groups with one control group 1(only feeding the basic diet)and three experimental groups(added 0.01%,0.02%,0.03%expanded chitosan in the basic diet).Each group has 3 replicates in,and every replicates has six heads per repetition(male and female each occupy half).During the trial period(7 days pre-test period,40 days formal trial period),the test piglets were managed uniformly and provided with free drinking water and feeding.According to our investigation,following conclusions are summarized:(1)The physicochemical properties of the expanded chitosan and unexpanded chitosan were determined by twin-screw extrusion treatment.The results shown that the physical and chemical properties of chitosan changed after extrusion.The odor,color and shape of chitosan were changed from grayish white and fine powder without any odor,pearly luster to charred scent,dull earthy brown,porous fluffy floc.Moisture absorption,moisturizing and acid dissolution performance were significantly enhanced(P<0.05),and bulk density was significantly decreased(P<0.05).The X-ray diffraction pattern shown that the semi-crystalline structure of chitosan was destroyed and the crystallinity was significantly reduced.Scanning electron microscopy(SEM)images revealed that the surface of the chitosan after expanded become uneven and had fluffy structure and more pores.(2)Through,studying the effect of in vitro expansion of chitosan on pathogenic bacteria,it was found that expanded chitosan had stronger killing effect on pathogenic Escherichia coli ATCC25922 and Staphylococcus aureus ATCC6538 compared with chitosan.The double-layer agar expansion test shown that the inhibition zone diameter(17.8 mm,19.7 mm)of the expanded chitosan against Escherichia coliATCC 25922 and Staphylococcus aureus ATCC 6538 was significantly greater than that of chitosan(9.6mm,12.5 mm).The MIC test shown that the MIC(3.6 mg/mL,3.6 mg/mL)of the expanded chitosan was significantly lower than that of chitosan(6.3 mg/mL,4.7 mg/mL).The MBC test shown that the expanded chitosan had evident,lower MBC(6.3 mg/mL,4.7 mg/mL)for both bacteria than chitosan(8.4 mg/mL,6.3mg/mL).The bactericidal kinetics test shown that the bactericidal effect of expanded chitosan and chitosan on both bacteria shown a time-dependent increase trend,while the bactericidal strength of expanded chitosan was obviously higher than that of chitosan.SEM images indicated that the expanded chitosan destroyed the intact cell membrane structure of the bacteria and then caused the contents of the cells to collapse and leak,and finally resulted in the ultimate death of the bacteria.(3)The effect of expanded chitosan on the growth index of small weaned piglets and the morphology of small intestine showed that the effect of expanded chitosan in the diet was 0.02%.Comparing with the control group,the average daily gain,the villus height of duodenum,jejunum and ileum,the ratio of the villus height to the crypt depth of weaned piglets in 0.02% group,were increased by 17.76%,19.85%,21.79%,26.29,78.69%,89.76% and 76.60%,respectively(P<0.05).And the feed-to-weight ratio of 0.02% weaned piglets and the depth of crypts of duodenum,jejunum and ileum were reduced by 22.48%,32.86%,35.95% and 28.29%,respectively(P<0.05).(4)The test results of expanded chitosan on nutrient digestibility and digestive enzyme activity of weaned piglets showed that the effect of puffed chitosan in the diet was 0.02%.Comparing with the control group,the apparent digestibility of crude ash and phosphorus in the diet of 0.02% weaned pigs and the amylase activity in the duodenum,jejunum and ileum were increased by 14.60%,20.49%,12.00%,23.89%and 17.18%,respectively(P<0.05).And the apparent digestibility of crude fat and the activity of lipase in duodenum,jejunum and ileum of 0.02% group weaned pigs were decreased by 8.67%,13.98%,18.06%and 15.07%,respectively(P<0.05). |
