Randomized efficacy trials of long-acting oxytetracycline in neonatal pigs

Prophylactic efficacy of 100 mg of long-acting oxytetracycline (OTC) given i/m to newborn piglets within 12 h of birth was evaluated in a herd. The herd had a history of increased newborn mortality, diarrhoea, foot abscess, and arthritis in nursing piglets. Two trials were conducted with litters and individual piglets. In both trials, OTC treatment failed to reduce mortality, diarrhoea, or arthritis or the need for subsequent antimicrobial therapy. Preweaning weight gains were not increased in treated piglets. However, in the individual piglet trial, foot abscess rates were significantly lower in treated piglets (3.7%) than in untreated pigs (8%). Aerobic bacteria isolated from piglets with diarrhoea, arthritis, or foot abscess had minimum inhibitory concentrations for OTC of ≥64 µg/ml or were classed as resistant on the basis of disk-diffusion tests.