Effects of Mycoplasma hyopneumoniae vaccination in pigs co-infected with M hyopneumoniae and porcine circovirus type 2

Objectives: To evaluate clinical and production parameters in pigs vaccinated with commercially available Mycoplasma hyopneumoniae (M hyo) bacterins, then co-infected with M hyo and porcine circovirus type 2 (PCV2). Materials and methods: Weaned pigs (n = 296) were each vaccinated with one of three M hyo bacterins or a placebo and challenged 3 and 5 weeks after the second vaccination with M hyo and PCV2, respectively. A subset of pigs, necropsied 2 or 4 weeks after PCV2 challenge, were evaluated for clinical signs, lesions, PCV2 serum levels, and M hyo in bronchial alveolar lavage fluids. Anti-body titers to M hyo and PCV2 and average daily gain (ADG) were determined periodically during the trial. Estimated carcass value was determined at market weight. Results: In the placebo group, the challenge caused severe respiratory disease associated with M hyo and PCV2. There was no evidence of vaccine-enhanced PCV2 associated disease, in that the vaccine and placebo groups did not differ in PCV2 serum levels, severity of PCV2 lesions, or incidence of PCV2-associated disease. Vaccinated groups had lower lung lesion scores at necropsy 2 weeks post challenge and higher body weights and ADG at the study conclusion. Implications: When short-term clinical and long-term production parameters are evaluated, control of M hyo infection by M hyo vaccination is an important tool in reducing respiratory disease and production losses in herds infected with both PCV2 and M hyo. Under the conditions of this study, M hyo, vaccination does not enhance disease associated with PCV2 infection.