Escherichia coli load in the gut and weight gain in broilers: insights from a systematic review and meta-analysis

Escherichia coli, a gram-negative bacterium is one of the dominant members of the commensal microbiota in young broiler chickens (Ocejo et al., 2019). However, under certain circumstances, it can also cause colibacillosis, which is an economically important disease. In studies aimed at improving broiler chicken production, the increase in the load of the phylum Proteobacteria that includes E. coli, is regarded as an indicator of dysbiosis and poor gut health (Diaz Carrasco et al., 2019; Shin et al., 2015), contradicting the role of the organism as a commensal bacterium (Rychlik, 2020) Therefore, the precise link between E. coli load and broiler growth performance has remained elusive.

This systematic review was conducted to investigate whether there is an association between E. coli load in different gut sections of broiler chickens and body weight gain at different stages of growth. We conducted a comprehensive search following Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines to collect eligible peerreviewed published articles from PubMed and the Web of Science. Among the initial pool of 2,108 articles screened, 60 were deemed suitable for inclusion in the final meta-analysis. Criteria for inclusion were peer-reviewed articles in English, experimental studies with broiler chickens as subjects, inclusion of body weight and E. coli in counts presented as averages with SD or SEM, inclusion of a negative control group, and maximum chicken age of 42 days.

To address the inherent variability among studies, standardized procedures were adopted during data extraction. Ultimately, we focused on records from the ileum and caecum at 21, 35, and 42 days of age in untreated negative control groups of broilers from thae selected studies. Random effects metaregression models were constructed for each gut section and age combination, using a significance level of 0.05. The residuals of each final model were visually checked for normality, and bubble plots were generated to show the relationship between E. coli count and weight gain at the study level.

The results unveiled a positive association between E. coli count in both ileum and caecum at 21 days of age and the weight gain in broiler chickens. However, no significant associations were observed at 35 and 42 days of age. In summary, the association between E. coli load and body weight gain in broiler chickens appears to be age dependent. This dependency could be attributed to the relative dominance of E. coli during the early stages of the birds’ development when microbial diversity is limited. The dynamic association between the E. coli load and weight gain underscores the importance of carefully assessing commensal E. coli to support bird health during the critical early growth phases, while considering its potential pathogenicity.