EVALUATION OF THE EFFECTS OF NURSERY DEPOPULATION ON THE PERSISTENCE OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS AND THE PRODUCTIVITY OF 34 FARMS

Nursery depopulation has been described as an effective strategy for i mproving the performance of weaned pigs, In order to assess whether th e strategy was effective under a wide range of conditions, a study was carried out on 34 farms in the USA, Four groups with different depopu lation protocols were designed on the basis of the location of the dep opulated facility (on site vs off site) and the period for which the n ursery remained empty (seven days vs 14 days), The changes in average daily liveweight gain, percentage mortality, feed efficiency and treat ment cost per pig produced were assessed 12 months before and after nu rsery depopulation. The ability to eliminate porcine reproductive and respiratory syndrome (PRRS) virus was examined by indirect fluorescent antibody testing of the nursery pigs, Significant improvements (P<0.0 001) were detected in both average daily gain and percentage mortality after depopulation when the differences within an individual group we re analysed, but no significant differences (P>0.14) were observed bet ween the study groups. Serological testing indicated that antibodies t o PRRS virus were still present in 14 of the 34 farms after depopulati on.