Virginiamycin: Lack of interference with Lawsonia intracellularis immunization

Abstract

Objective: To determine if concurrent administration of virginiamycin interferes with immunization efficacy of Enterisol Ileitis (Boehringer Ingelheim Vetmedica, Inc, St Joseph, Missouri). Materials and methods: Eighty-eight weanling pigs were divided into four groups: a strict negative, non-challenged, non-vaccinated, non-medicated group (NCC), a challenged, non-vaccinated, non-medicated group (CC), a challenged, vaccinated, non-medicated group (VC), and a challenged, vaccinated, medicated group (VM). The VM group received in-feed virginiamycin at 11 g per tonne from Day 0 (4 weeks of age) through Day 27. Vaccinated groups were immunized with one dose of Enterisol Ileitis on Day 1. Virginiamycin administration continued for 28 days to determine whether it interfered with development of immunity generated by the vaccine. Challenged groups were administered an oral dose of mucosal homogenate containing virulent Lawsonia intracellularis (LI) on Day 31. Pigs were euthanized and necropsied on days 51 and 52 to evaluate intestinal lesions. Results: Significantly fewer macroscopic jejunal (P < .01) and ileal (P < .05) lesions were observed in VC and VM groups than in the CC group. Microscopic ileal immunohistochemistry scores in VC and VM did not differ, and both were significantly lower (P < .05) than in the CC group. During the vaccination phase when virginiamycin was administered, feed efficiency was best in VM (P < .001) and intermediate in VC (P < .001), compared to CC. Implications: Under the conditions of this study, administration of in-feed virginiamycin at 11 g per tonne does not interfere with the efficacy of concurrent immunization with Enterisol Ileitis.