Spread of an Experimental Derby Infection in Antibiotic-Treated or Vaccinated Piglets.

infections are a common reason for antibiotic treatment in pig production. Experimental studies in animals naturally infected with comparing the course of an experimental infection in piglets previously treated with tylosin or vaccinated against are scarce. A total of 72 seven-week-old -free pigs were taken from a herd with a history in piglet rearing. The pigs were divided into two groups with three replicates each. Animals had either been previously treated with tylosin (10 mg/kg body weight) for seven days (AB⁺VAC) or had been vaccinated as suckling pigs by drenching (EnterisolIleitis; ABVAC⁺). Two animals per replicate were primarily infected with Derby (1.04 × 10⁸ colony-forming units per animal). The detection of in faeces ( < 0.0001, odds ratio: 3.8364) and in the ileocaecal lymph nodes ( = 0.0295, odds ratio: 3.5043) was significantly more frequent in AB⁺VAC animals. Overall, the odds ratio for detecting in any substrate or organ was significantly higher in the AB⁺VAC group animals ( = 0.0004, odds ratio: 5.9091). Treatment with tylosin can significantly increase the spread of a infection, which is not observed after early vaccination.