Comparative Efficacy of Intramuscular and Intradermal Porcilis Lawsonia® Administration Under a Laboratory Challenge Model and Korean Field Conditions

Background/Objectives: Lawsonia intracellularis is a major enteric pathogen of swine that causes proliferative enteropathy, reduced growth performance, and economic losses. Although vaccination is an effective control strategy, comparative data on the efficacy of intramuscular (IM) and intradermal (ID) administration of inactivated L. intracellularis vaccines are limited. This study evaluated and compared the efficacy of Porcilis Lawsonia® administered by IM or ID routes under experimental challenge and Korean field conditions. Methods: In a laboratory challenge study, 24 L. intracellularis-negative piglets were assigned to IM-vaccinated, ID-vaccinated, or unvaccinated control groups (n = 8/group). Vaccinated pigs received Porcilis Lawsonia® and were orally challenged with L. intracellularis four weeks later. Clinical signs, average daily gain (ADG), antibody responses, bacterial shedding, and intestinal lesions were evaluated. In a field trial, 90 piglets from three commercial Korean farms were allocated to IM, ID, or control groups (n = 30/group) and monitored for growth performance, serological responses, and fecal shedding. Results: Under challenge conditions, both IM and ID vaccination significantly reduced clinical signs and fecal shedding while improving ADG and final body weight compared with controls. Vaccinated pigs developed significantly higher antibody responses before challenge. In field trials, both vaccination routes significantly increased body weight at 19 weeks of age and markedly reduced L. intracellularis shedding. No vaccine-related adverse effects were observed. Differences between IM and ID vaccination were generally not significant, although IM vaccination induced slightly higher antibody responses at 13 weeks of age under field conditions. Conclusions: Porcilis Lawsonia® administered by either IM or ID routes provided comparable protective efficacy against L. intracellularis infection, reducing bacterial shedding and improving growth performance under both experimental and field conditions. These findings support ID vaccination as an effective alternative to conventional IM administration.