Field evaluation of a live vaccine against porcine reproductive and respiratory syndrome in fattening pigs

A live vaccine based on a European isolate of porcine reproductive and resp iratory syndrome virus (Porcilis PRRS) was tested in this study in order to determine the protection of fattening pigs against the respiratory form of the syndrome under field conditions. Ten thousand pigs in an infected farm were vaccinated against PRRS virus at the age of 6 weeks and were compared with non-vaccinated pigs with respect to their health status, mortality, p erformance parameters (average daily gain, average daily feed intake, feed conversion ratio) and the presence of certain pathogens in their lungs. The results showed that treated pigs became ill less frequently and demonstrat ed reduced mortality compared with untreated ones. As compared with non-vac cinated animals, PRRS-vaccinated pigs also performed in a better way with r espect to the feed conversion ratio (P < 0.05) and average daily gain (P < 0.05), while feed intake was similar for both groups (P > 0.05). Bacteriolo gical examinations of the lungs revealed increased incidence of respiratory bacterial infection in untreated pigs compared with treated ones. A tenden cy for a faster antibody response was also detected in the vaccinees. The r esults of the present study show that immunization with a live vaccine does protect fattening pigs against the respiratory manifestations of PRRS.