Simple SummaryThe intestinal microbiota plays a vital role in nutrient digestion, pathogen exclusion, immune de-velopment, and subsequently animal productivity. However, specific microbes that are associated with animal growth are still unclear. Here we profiled the cecal microbiota to identify those bacteria that are linked to body weight gain of broiler chickens raised under typical commercial conditions. Several bacteria were found to show either a positive or negative association with body weight. These bacteria may be further explored to improve the growth performance of chickens and also as potential biomarkers for the selection of broiler chickens with different growth rates.AbstractThe intestinal microbiota is critically important for animal health and productivity. However, the influence of the intestinal microbiota on animal growth efficiency remains elusive. This current study was aimed at identifying the intestinal bacteria that are associated with the growth rate of broilers in a commercial production setting. Ross 708 broilers with extremely high, medium, and extremely low body weight (BW) were separately selected for each sex from a house of approximately 18,000 chickens on day 42. The cecal content of each animal was subjected to 16S rRNA gene sequencing for microbiota profiling. Our results indicate that a number of bacteria were differentially enriched among different groups of broilers, with several showing a significant correlation (p< 0.05) with BW in both sexes or in a sex-specific manner.Subdoligranulumwas drastically diminished in high-BW birds with a strong negative correlation with BW in both males and females. While oneAnaerobutyricumstrain showed a positive correlation with BW in both sexes, another strain ofAnaerobutyricumwas positively correlated with BW only in females. These sex-dependent and -independent bacteria could be targeted for improving the growth efficiency and may also be explored as potential biomarkers for the growth rate of broiler chickens.