Effects Of Antibiotic Additives On The Production Performance And Fecal Microbes Of Weaned Pigs

Currently,the use of antibiotics in livestock is a hot topic.The main issue of antibiotics abuse is the increase of the proportion of resistant bacteria or "superbugs" in the environment.However,antibiotics are very important medicine for protecting human health and can not be replaced today.Therefore,the EU and the United States issued some regulations to limit the use of antibiotics in animal husbandry in recent years.In China,antibiotics are mainly used as growth promoter and prevention or treatment diseases of veterinary drugs in pig production.However,how the growth-promoting effect of antibiotics?What the effect of antibiotics on weaned pig fecal microbes?Whether it would affect antibiotic resistance genes?These are very important questions and deserved careful study.Tetracyclines are broad-spectrum antibiotics with activity against both gram-positive and gram-negative bacteria.Since they have favorable antimicrobial properties and no major adverse side effects,tetracyclines are extensively utilized therapeutically for livestock.Chlortetracycline has favorable antibacterial activity and can promote animal growth.Previous studies have shown that chlortetracycline can promote the growth performances and regulate the gut microflora of pigs,but abuse of chlortetracycline increased the abundance of tetracycline resistance genes.In the present experiment,I investigated the effects of subtherapeutic chlortetracycline(75 ppm)combination supplementation on the pig production performances,fecal microbes and the relative abundance of tetracycline resistance genes(TRGs)in feces of weaned pigs.In this experiment,four hundred 35-day-old weaned piglets(Duroc sires×(Landrace ×Large White)dams)were selected and randomly assigned to 8 groups:CT,Control group fed basal diet(without antibiotics);CTC,fed 75 mg/kg chlortetracycline in basal diets;BC,fed 40 mg/kg bacitracin zinc and 20 mg/kg colistin sulphate in basal diets;CBC,fed 75 mg/kg chlortetracycline,40 mg/kg bacitracin zinc and 20mg/kg colistin sulphate in basal diets;CS,fed 75 mg/kg chlortetracycline and 50 mg/kg Macleaya cordata extracts;CO,fed 75 mg/kg chlortetracycline and 100mg/kg olaquindox in basal diets;COE,fed 75 mg/kg chlortetracycline,100 mg/kg olaquindox and 20mg/kg enramycin in basal diets;COV,fed 75 mg/kg chlortetracycline,100 mg/kg olaquindox and 15mg/kg virginiamycin in basal diets.There were 3 replicates(pens)per group and 16-17 piglets per pen.At the 28th day of experiment,a total of 120 pigs(5 pigs per pen)were randomly selected to collect blood samples;72 pigs(3 pigs per pen)were randomly selected to collect the fresh feces individually.The present study has three parts as follows:1 Effects of antibiotics additives on the production performances and serum immune parameters of weaned pigsThe aim of this study was to evaluate the effects of subtherapeutic chiortetracycline combination supplementation on the production performances(ADG,ADFI and F/G),survival rate,morbidity of diarrhea and serum immune parameters(IgG、IgM、IgA、IL-12 and IFN-γ)of weaned pigs.The results showed that the experimental pig were healthy,the morbidity of diarrhea in each group was 0.05%-3.04%.Antibiotics additives at subtherapeutic levels had no significant effects on the diarrhea rate,ADG,ADFI and F/G of weaned pigs.The CS(chlortetracycline and Macleaya cordata extracts)group had the greatest ADQ the CO(chlortetracycline and olaquindox)group had the lowest ADG,and there was a significant difference between these two groups.Compared with the CT group,subtherapeutic antibiotics additives reduced the concentrations serum immunoglobulin and cellular immune factors,but they are all within the normal range.Overall,subtherapeutic antibiotics additives had no significant effects on the growth performances of weaned pigs,but reduced the concentrations of serum immunoglobulin and cellular immune factors,which were in the normal ranges.2 Effects of antibiotics additives on the abundance and diversity of fecal microbes in weaned pigsIn this experiment,16S rRNA high-throughput sequencing was used to analyze the effects of subtherapeutic antibiotics additives on the abundance and diversity of fecal microbes in weaned pigs.The results showed that chlortetracycline combination with olaquindox and enramycin or chlortetracycline combination with olaquindox and virginiamycin reduced the diversity of fecal microbes.Compared with the CT group,the diversity of fecal microbes had no significant differences in other five groups.They also increased the abundance of bacteroidetes significantly in the Phylum;increase the abundance of Prevotella significantly in the Genus.Overall,the effect of subtherapeutic antibiotics additives on the diversity and abundance of fecal microbes are finite.3 Effects of antibiotics additives on the relative abundance of ARGs in feces of weaned pigsIn this experiment,real-time PCR was used to analyze the effects of subtherapeutic antibiotics additives on the relative abundance of ARGs in feces of weaned pigs.The results showed that the relative abundances(tet/16s rRNA gene copy numbers)of six TRGs(tetA,tetC,tetL,tetO,tetw and tetX)were between 1.5×10-4 and 2.0×10-1.The TRGs have a widespread existence in fecal microbes of pigs.Compare with CT group,feeding of antibiotics for 28 days increased the abundances of TRGs in the feces.Compared with feeding chlortetracycline alone,the combination of antibiotics suppressed the increase of a part of TRGs.Overall,subtherapeutic antibiotics additives increased the abundances of TRGs in the feces of weaned pigs,but the combination of different antibiotics suppressed the increase the abundance of a part of TRGs,which protected the environment.In summary,compared with the CT group,subtherapeutic chlortetracycline combination with other antibiotic additives or Macleaya cordata extracts had no significant effects on the grwoth performance of weaned pigs.The CS(chlortetracycline and Macleaya cordata extracts)group had the greatest ADG,the CO(chlortetracycline and olaquindox)group had the lowest ADG,there were a significant difference between these two groups.Compared with the CT group,subtherapeutic antibiotics additives reduced the concentrations serum immunoglobulin and cellular immune factors,but they were all within the normal ranges.The effects of subtherapeutic antibiotics additives on the diversity and abundance of fecal microbes were limited,but the combination of different antibiotics suppressed the increase of abundances of a part of TRGs.These results suggest that subtherapeutic antibiotics additives had limited effects on the production performance of healthy weaned pigs,the diversity and abundance of fecal microbes,but they could suppressed the increase the abundance of a part of TRGs.