Effects of Different Inoculation Doses on Growth Performance, Daily Feed Intake, Gut Health, Gut Microbiota, Foot Pad Dermatitis, and Gene Expression in Broilers Raised in Floor Pens for 35 Days

The study was conducted to investigate the effects of different inoculation doses on the growth performance, gut ecosystem, and body composition of broilers in floor pens for 35 days. A total of 750 15-day-old broilers were allocated to five experimental groups with six replicate pens. The five experimental groups included unchallenged control (CON); dose 1 (ED1): : 31,250/: 6250/: 6250; dose 2 (ED2): : 62,500/: 12,500/: 12,500; dose 3 (ED3): : 125,000/: 25,000/: 25,000; and dose 4 (ED4): : 250,000/: 50,000/: 50,000. On D 21, BW were linearly reduced by increased inoculation doses ( < 0.01). On D 35, the challenge groups had significantly lower BW compared to the CON group. Increased inoculation doses linearly decreased crude fat (CF) ( < 0.01) on D 21. Increased inoculation doses tended to increase the relative abundance of the phylum Proteobacteria ( = 0.098) on D 21. On D 35, lean:fat was linearly reduced by increased inoculation doses ( < 0.05). infection negatively influenced growth performance and gut health in broilers in the acute phase, and the negative effects were prolonged to D 35 in floor pen conditions.