A FIELD TRIAL TO EVALUATE A MYCOPLASMA-HYOPNEUMONIAE VACCINE - EFFECTS ON LUNG LESIONS AND GROWTH-RATES IN SWINE

A killed Mycoplasma hyopneumoniae vaccine was evaluated in a single sw ine herd in which the farrowing barn and weaner rooms were on one Myco plasma-free farm, while the growing and finishing barn was on a separa te farm on which Mycoplasma was present. The study was carried out in a cohort of pigs born in a 12-week period, Pigs born in 6 of the 12 wk were vaccinated and the rest were left as controls. The vaccine was a dministered twice at approximately 3 and 6 wk of age. Carcass characte ristics, lung lesions, and growth rates were recorded on 893, 390, and 220 pigs, respectively. The vaccine reduced the prevalence of pneumon ic lesions in slaughter hogs from 69% to 36% (P < 0.001). It also appe ared to reduce the prevalence of pleuritis from 20% to 13%, but the di fference was only statistically significant at P = 0.07. The vaccine h ad no effects on carcass characteristics except that carcasses of vacc inated pigs were, on average, 1 kg heavier than those of nonvaccinated pigs, and a smaller percentage of vaccinated pigs were shipped ''ligh t'' (carcass weight <70 kg). Two methods were used to estimate the eff ect of the vaccine on growth rates (as measured by days to 80 kg carca ss weight) resulting in estimates of 11 and 2 d reduction attributable to vaccination, respectively. The latter estimate was probably an und erestimate for reasons discussed in the paper.