Broiler chicks were spray treated on the day of hatch with titrated dosages (106, 107, or 108 anaerobic CFU) of a characterized competitive exclusion culture (CF3) and challenged orally on day 3 with 104 CFU of Salmonella typhimurium. On day 10, cecal contents from control and CF3-treated chicks were cultured for S. typhimurium to determine the minimal efficacious dosage of the CF3 culture. The experiment was repeated in three replicated trials. Resistance to Salmonella cecal colonization was dosage related and progressively enhanced at the 107- and 108-CFU dosages compared with the 106-CFU dosage. The 107-CFU dosage was selected as the minimal effective dosage and evaluated for efficacy during a 43-day broiler growout study. Six hundred broilers were spray treated on the day of hatch and compared with 600 Controls. One-half of the control and CF3-treated birds were challenged orally on day 3 with 104 CFU of S. typhimurium and designated “seeders.” The remaining unchallenged birds were designated “contacts.” Compared with the Controls, the recovery of Salmonella cells from the ceca of the CF3-treated broilers was significantly decreased (P < 0.01) in the challenged seeders on days 21 and 43 of growout. Salmonella contamination of floor pen litter was significantly reduced (P < 0.05) in pens of CF3-treated birds compared with Controls. The transmission of Salmonella cells from seeder to contact birds in the same pens was decreased significantly (P < 0.01). The results indicated that treatment of broiler chicks on the day of hatch with the 107-CFU dosage of CF3 culture effectively increased resistance to S. typhimurium challenge during growout to market age.

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