Evaluation of Mycoplasma hyopneumoniae inactivated vaccine in pigs under field conditions.

An inactivated vaccine prepared from broth culture supernatant of Mycoplasma hyopneumoniae with an aluminum adjuvant was evaluated in three herds (herd A: specific pathogen-free herd, herd B: high health status herd with no clinical signs of respiratory infection, herd C: low health status herd with serious epidemiological and economical problems). A total of 212 pigs from the three herds were divided into two groups. One group was injected twice with the vaccine at 4-week intervals and the other was a control group. No adverse reactions were noted following the vaccinations either systematically or locally in any of the vaccinated pigs from any of the herds. In herd A, the vaccination provided antibody response within 4 weeks after the second vaccination and antibody responses continued for more than 12 weeks. In herds B and C, the number of pigs with lung lesions, mean percentage of lung lesions, and the numbers of M. hyopneumoniae recovered from pigs at slaughter in the vaccinated group were significantly (P < 0.05) reduced compared to the control group. Furthermore, vaccination resulted in improved average daily weight gain (ADG), improved feed conversion ratio (FCR), and improved days to market weight in herd C, whereas no difference in growth performance was shown in herd B. It is suggested that the inactivated vaccine prepared from broth culture supernatant of M. hyopneumoniae is effective in reducing clinical signs and lung lesions. Also, vaccination resulted in improved growth performance in herds where clinical signs and economic losses were significant.