Association Between Load in the Gut and Body Weight Gain in Broiler Chickens: A Systematic Review and Meta-Analysis.

is one of the first commensal bacteria to colonize the chicken gut, where it predominates at an early stage of broiler chick life can potentially cause colibacillosis in chickens, spreading to extraintestinal systemic organs, which results in high economic losses in poultry industry, as well as a potential risk to public health. Many studies conducted to investigate the effectiveness of natural products as alternatives to antibiotics and to enhance the production performance in broiler chickens have assessed load in the chicken gut, but it is still unknown how the count is linked to broiler growth performance. A systematic search of published research articles, including key terms of interest such as broiler chickens, growth performance, and count, was conducted using two main databases (PubMed and the Web of Science). A random effects metaregression model was built to evaluate the association between count and weight gain in untreated groups of broilers (negative controls) from eligible studies. Of 2108 articles in the initial screening, 60 were included in the final meta-analysis. After data extraction, records from the ileum and cecum at 21, 35, and 42 days of age were considered for the meta-analysis. The meta-analysis showed that the average count in both the ileum and cecum at 21 days of age was positively associated with the average weight gain in the studied broiler chickens, while no statistically significant associations were found at 35 and 42 days of age. In conclusion, the positive association between load and body weight gain in young broiler chickens may be attributed to the relative dominance of in the gut of this age group when the microbial population is less diverse. The dynamic association between the production performance and the load of that has dubious pathogenic potential suggests the importance of careful assessment of commensal to develop strategies to enhance production, particularly in young broiler chickens.