The Effect Of Bacillus Subtilis YK-1R On The Development Of Weaned Piglet Gut Microbiota

The gastrointestinal(GI)is a complex and enormous ecosystem.Host and gut microbes exchange actively metabolic molecules which produced by them respectively and influence with each other via enterohepatic circulation,intestinal tract barrier and other physiological and anatomic connections.Thus gut microbiota plays a critical role on maintaining host healthy.Early weaned piglets are vulnerable to diarrhea because of weaning stress and immaturity of intestinal function.However,it is not well understood on the composition and succession of piglet gut microbiota during the weaning transition.Because early weaned piglets are susceptible to weaning stress syndrome,antibiotics was added to feed with subtherapeutic doses frequently to improve health status of weaned piglets.However,more and more resistant bacteria were observed in environment due to chronically abuse of antibiotics and antibiotic resistance genes in bacteria can transfer to human via food chains which will threaten human health.Searching alternatives of antibiotics draws a great interesting.This thesis studied the composition and succession of piglet gut microbiota from 10 days before weaned to 21 days after weaned,explored whether probiotics of Bacillus subtilis YK-1R can improve the health status of weaned piglets instead of antibiotics,and characterize modulation of piglet gut microbiota by Bacillus subtilis YK-1R.First,total 17 commercial piglets were studied in a pig farm.Fresh feces of piglets were collected in 10 days before weaned,weaned day,10 days after weaned,21 days after weaned by rectal massage.Fecal bacterial composition was assessed by 16 S rRNA gene V3-V4 regions sequencing by Illumina Miseq platform.The result shows that the microbiota of suckling piglets was mainly represented by Fusobacterium,Lactobacillus,Bacteroides,Escherichia/Shigella and Megasphaera.This pattern contrasted with that of Clostridium sensu stricto,Roseburia,Paraprevotella,Clostridium XIVa and Blautia,which were major representative genera after weaned.The gut microbiota of piglets shifted quickly after weaned and reached relatively stable level in 10 days after weaned.The alpha diversity increased significantly with the age of piglets.Sixteen genera and twelve OTUs occurred in all samples regardless of age,which represent core functional phylotypes of piglet gut.These phylotypes may play a vital role in keeping health of piglets.The result of coabundance network analysis of 85 key OTUs responding to age and weaning suggest that Fusobacterium and Lactobacillus which was abundant in suckling piglets was positively correlated with each other.Potential interaction may exist between this two OTUs.Second,we explored whether Bacillus subtilis YK-1R can replace of antibiotics as feed additives to improve piglet health status via two experiments.The first experiment was started on three days after weaned and piglets were weaned on 21 days after birth.The result showed that Bacillus subtilis YK-1R can improve growth performance,reduce diarrhea rate and modulate gut microbiota of weaned piglets.However,the first experiment was small in scale and we also want to explore the effect of Bacillus subtilis YK-1R and antibiotics on suckling piglet gut microbiota,so we conducted the second experiment.The experiment began on 10 days before weaned and piglets were weaned on about 24 days after birth.The result revealed that there were no significant differences on piglet growth performance,diarrhea rate between control group,probiotics group and antibiotics group.The gut microbiota structure also showed no significant difference between three groups.The inconsistent result between two experiments may attribute to different health condition of investigated piglets.Piglets in first experiment had stronger weaning stress,higher diarrhea incidence during the whole investigated period.Probiotics and antibiotics have no obvious effect on health piglets.Thus further research is need to explore the beneficial effect of Bacillus subtilis YK-1R on weaned piglets.Next we can use diarrheal piglet model which infected by pathogens to assess this probiotics.In conclusion,first,we delineated the development of piglet gut microbiota during the weaning transition.This study helps us understand the maturing development of gut microbiota in commercial piglets.Second,we explored whether Bacillus subtilis YK-1R can improve health condition of early weaned piglets instead of antibiotics preliminarily.