Lawsonia intracel/ularis (L. i.), an ubiquitous pathogen, is well known as the causative agent of ileitis, a major gut-related health disease in pork production. Two approaches exist to control the ileitis-induced loss: Therapy by antibiotics or prophylaxis by vaccination. This field study was conducted to answer the question: Docs a curative treatment with antibiotics improve performance as good as protection by vaccination in a L. intracellularis infected herd?