Effects of Mycoplasma hyopneumoniae vaccine on pigs naturally infected with M. hyopneumoniae and porcine reproductive and respiratory syndrome virus.

The effects of a single-dose Mycoplasma hyopneumoniae vaccine was studied in growing pigs. Each of 24 vaccinated cohorts of approximately 1200 pigs reared in separate barns was matched by time, farm site, and sex with unvaccinated cohorts. Pigs were naturally exposed to M. hyopneumoniae and porcine reproductive respiratory syndrome virus (PRRSv). Daily weight gain was 42 g per pig per day higher and mortality rate was 15.2/1000 pigs lower for vaccinated cohorts. Age at PRRSv onset was associated with mortality rate, but did not modify vaccine effects. M. hyopneumoniae vaccination was effective in promoting growth in spite of concurrent PRRSv infection.