| Strain screening is the focus of research and development of microecological agents.Host-specific lactobacillus are considered as excellent candidates for making microecological agents.Therefore,the purpose of the experiment was to isolate and screen the specific homologous Lactobacillus with growth-promoting effect on duck growth,in order to provide scientific guidance on the healthy breeding of meat ducks.Experiment 1.The lactobacillus strains were isolated and screened from the gut of healthy duck through analyses of xford cup bacteriostasis,bile salt tolerance,simulated gastrointestinal,drug resistance,and growth curve.The isolated strains were identified by morphological observation,analyses of physiological and biochemical characteristics and 16 s r RNA sequencing followed by Atmospheric and room temperature plasma mutagenesis(ARTP)and fermentation process optimization.The results were as follows:(1)A strain of Lactobacillus with strong bacteriostatic effect against Escherichia coli,Salmonella and Staphylococcus aureus was isolated and screened from healthy duck gut.The strain displayed fast growth rate,strong acid production ability,and could tolerate 0.1% bile salt,survive 100% after simulated gastric juice and intestinal liquid treatment for 2 h,and was sensitive to chloramphenicol,penicillin,ceftriaxone three antibiotic drugs.The strain was gram staining positive,with spherical rod-like,arranged in pairs or chain-like.Based on the results of the physiological and biochemical characteristics,this strain was identified as lactobacillus,and then identified as Lactobacillus reuteri strain by 16 s r RNA sequencing.(2)Under 37℃,the strain grew very fast,and subjected for fermentation at 1% inoculation,with the first 1-2 h as reaching growth latency period,the later 2 h as logarithmic growth period,and last 8-10 h as platform period.(3)The optimum ARTP mutagenesis time of the strain was 45 s,and the mortality rate was 93.4%.After mutagenesis,the inhibiting rate of the strain 277 was increased by 10.64% against Escherichia coli,by9.42% against Salmonella and by 9.20% against Staphylococcus aureus.(4)The optimized medium and conditions of strain 277 of Lactobacillus reuteri strain were as follows: glucose 20 g/L,yeast powder 20 g/L,soybean peptone 10 g/L,beef extract 5g/L,diammonium citrate 2 g/L,sodium acetate 5 g/L,manganese sulfate 0.05 g/L,Tween 80 g/L.The optimum fermentation conditions were maintained at p H 6.0-7.5,37℃,and the proportion of fermentation broth to bottle capacity of 60%.Experiment 2.A total of 1680 healthy muscovy ducks of 21 days old were randomly divided into 4 groups according to the body weight.The 4 groups included group A(negative control group,feeding the basal diet),group B(test group 1,adding500 mg/kg of Bacillus subtilis to the base diet),C group(test group 2,adding 500mg/kg of Lactobacillus reuteri strain 277 to base diet)and D group(test group 3,add500 mg/kg of Bacillus subtilis and Lactobacillus reuteri strain 277 to the basal diet).The effects of Lactobacillus reuteri strain on growth performance,immune organ index and slaughter performance of muscovy duck were studied.The results were as follows :(1)In terms of growth performance,compared with the control group(A group),the average daily weight gains at 21-50 days of groups B,C,and D were increased significantly(P<0.05%)by 3.25%,2.60% and 3.14%,respectively,and the feed intake to weight gain ratio of groups B,C,and D were decreased(P<0.05%)by 2.65%,1.75% and 2.65%,respectively.The survival rates of each test group were significantly higher than those in group A(P<0.05),and groups B and D had higher survival rates than those in group C.(2)At 50 days of age,the thymus indexes of the groups B and D two were significantly higher than the other groups(P<0.05),with increase by 11.27% and 13.09%,respectively.(3)In terms of carcass traits,the percentages of thigh muscle were significantly higher in groups B,C,and D than in A group(P<0.05),which increased by 14.34%,25.41%,and 34.97%,respectively,and C,D group significantly higher than B groups(P<0.05).The groups B,C,and D had decreased abdominal fat rate by 13.52%,19.29%,and 11.90%compared with group A(P<0.05).Conclusion: A strain of Lactobacillus with strong bacteriostatic effect against Escherichia coli,Salmonella and Staphylococcus aureus was isolated and screened from healthy duck gut.The strain displayed fast growth rate,strong acid production ability,and could tolerate 0.1% bile salt,survive 100% after simulated gastric juice and intestinal liquid treatment for 2 h,and was sensitive to chloramphenicol,penicillin,ceftriaxone three antibiotic drugs.Based on the results of the physiological and biochemical characteristics,this strain was identified as lactobacillus,and then identified as Lactobacillus reuteri strain by 16 s r RNA sequencing.After ARTP mutation,a strain 277 with stronger antibacterial ability was screened.The culture medium and culture conditions of 277 strain were optimized.The results of animal experiment showed that Lactobacillus reuteri strain 277 could significantly improve the growth performance,immune organ index and slaughter performance of Muscovy duck,and the effect of compound use with bacillus was better. |
