The present study explored whether the use of group medication with antibiotics in a Danish pig herd was reduced after vaccination of the pigs against proliferative enteropathy (PE) caused by Lawsonia intracellularis. 7900 pigs originating from a single commercial sow herd were vaccinated against L. intracellularis, whereas 7756 pigs were kept as non-vaccinated controls. The pigs were included batch-wise in the study with every second batch being vaccinated. In the vaccinated batches, the consumption of oxytetracykline to treat PE was reduced by 79%, with a significantly lower number of pigs being treated (P < 0.0001). Vaccination also resulted in a highly significant improvement of average daily weight gain (+ 46 g/day; P = 9.55 x 10(-31)) and carcase weight (+ 1.25 kg; P = 4.54 x 10(-05)) as well as a shortened fattening period (-8 days; P = 2.01 x 10(-45)).