Farmed chickens often suffer from intestinal inflammation which negatively affects their feed intake, digestion, and growth performance. The gut microbial community has a known close relationship with growth performance, but how, or if, this microbiota influences intestinal inflammation is not yet known. To test this, researchers examined the microbiota in young chickens, focusing on the jejunum section of the gut. They found that 7-week-old chickens with high body weight tended to have a microbiota dominated by gram-positive bacteria, like Lactobacilli. But lower-body-weight chickens had a microbiota dominated by gram-negative bacteria, like Escherichia-Shigella. Gram-negative bacteria carry endotoxin (lipopolysaccharide), and consequently, these lower body weight chickens had more of it in their bloodstream. These elevated lipopolysaccharide levels activated inflammatory cytokines in the jejunum, causing damage to the gut barrier. But these effects were tied to the early colonization of harmful bacteria in the gut. Transferring the fecal microbiota from high-body-weight adult chickens into day-old chicks mitigated the inflammatory response and improved their growth performance. These results suggest that fecal microbiota transfer may be a useful strategy to avoid intestinal inflammation and improve growth performance in chickens.