Intestinal Microbiota of Broiler Chickens As Affected by Litter Management Regimens

The diversity of bacterial floras in the ilea and ceca of chickens that were fed a vegetarian corn-soy broiler diet devoid of feed additives was examined by analysis of 1,230 partial 16S rRNA gene sequences. Nearly 70% of sequences from the ileum were related to those of Lactobacillus, with the majority of the rest being related to Clostridiaceae (11%), Streptococcus (6.5%), and Enterococcus (6.5%). In contrast, Clostridiaceae-related sequences (65%) were the most abundant group detected in the cecum, with the other most abundant sequences being related to Fusobacterium (14%), Lactobacillus (8%), and Bacteroides (5%). Statistical analysis comparing the compositions of the different 16S rRNA libraries revealed that population succession occurred during some sampling periods. The significant differences among cecal libraries at 3 and 7 days of age, at 14 to 28 days of age, and at 49 days of age indicated that successions occurred from a transient community to one of increasing complexity as the birds aged. Similarly, the ileum had a stable bacterial community structure for birds at 7 to 21 days of age and between 21 to 28 days of age, but there was a very unique community structure at 3 and 49 days of age. It was also revealed that the composition of the ileal and cecal libraries did not significantly differ when the birds were 3 days old, and in fact during the first 14 days of age, the cecal microflora was a subset of the ileal microflora. After this time, the ileum and cecum had significantly different library compositions, suggesting that each region developed its own unique bacterial community as the bird matured.

The objective of this study was to generate a phylogenetic diversity census of bacteria identified in the intestinal tract of chickens and turkeys using a naïve analysis of all the curated 16S rRNA gene sequences archived in public databases. High-quality sequences of chicken and turkey gastrointestinal origin (3,184 and 1,345, respectively) were collected from the GenBank, Ribosomal Database Project, and Silva comprehensive ribosomal RNA database. Through phylogenetic and statistical analysis, 915 and 464 species-equivalent operational taxonomic units (defined at 0.03 phylogenetic distance) were found in the chicken and the turkey sequence collections, respectively. Of the 13 bacterial phyla identified in both bird species, Firmicutes, Bacteroidetes, and Proteobacteria were the largest phyla, accounting for >90% of all the sequences. The chicken sequences represent 117 established bacterial genera, and the turkey sequences represent 69 genera. The most predominant genera found in both the chicken and the turkey sequence data sets were Clostridium, Ruminococcus, Lactobacillus, and Bacteroides, but with different distribution between the 2 bird species. The estimated coverage of bacterial diversity of chicken and turkey reached 89 and 68% at species-equivalent and 93 and 73% at genus-equivalent levels, respectively. Less than 7,000 bacterial sequences from each bird species from various locations would be needed to reach 99% coverage for either bird species. Based on annotation of the sequence records, cecum was the most sampled gut segment. Chickens and turkeys were shown to have distinct intestinal microbiomes, sharing only 16% similarity at the species-equivalent level. Besides identifying gaps in knowledge on bacterial diversity in poultry gastrointestinal tract, the bacterial census generated in this study may serve as a framework for future studies and development of analytic tools.

With increasing pressures to reduce or eliminate the use of antimicrobials for growth promotion purposes in production animals, there is a growing need to better understand the effects elicited by these agents in order to identify alternative approaches that might be used to maintain animal health. Antibiotic usage at subtherapeutic levels is postulated to confer a number of modulations in the microbes within the gut that ultimately result in growth promotion and reduced occurrence of disease. This study examined the effects of the coccidiostat monensin and the growth promoters virginiamycin and tylosin on the broiler chicken cecal microbiome and metagenome. Using a longitudinal design, cecal contents of commercial chickens were extracted and examined using 16S rRNA and total DNA shotgun metagenomic pyrosequencing. A number of genus-level enrichments and depletions were observed in response to monensin alone, or monensin in combination with virginiamycin or tylosin. Of note, monensin effects included depletions of Roseburia, Lactobacillus and Enterococcus, and enrichments in Coprococcus and Anaerofilum. The most notable effect observed in the monensin/virginiamycin and monensin/tylosin treatments, but not in the monensin-alone treatments, was enrichments in Escherichia coli. Analysis of the metagenomic dataset identified enrichments in transport system genes, type I fimbrial genes, and type IV conjugative secretion system genes. No significant differences were observed with regard to antimicrobial resistance gene counts. Overall, this study provides a more comprehensive glimpse of the chicken cecum microbial community, the modulations of this community in response to growth promoters, and targets for future efforts to mimic these effects using alternative approaches.