Abstract
BACKGROUND: PRRS is a viral disease of pigs and sows that is one of the most costly to the pig industry worldwide. The disease can be controlled by focusing on different aspects. One of them is the vaccination of piglets, which is more controversial and difficult to manage than the vaccination of sows. However, pig producers could consider a piglet vaccination strategy if it reduces the negative clinical disease and improves zootechnical performance, decreases the probability to be infected and/or reduces the spread of the virus once the vaccinated piglet is infected. The efficacy of a novel PRRS modified live vaccine (Ingelvac PRRSFLEX® EU) was studied in a blinded, side-by-side placebo controlled field study of piglet vaccination including piglets weaned for three consecutive weeks (week groups 1, 2 and 3). RESULTS: This study established that PRRS piglet vaccination resulted in significantly better weight gain, seen as early as 4 weeks after vaccination, in naturally challenged pigs. Vaccine efficacy was supported by statistically significant increases in Average Daily Weight Gain (ADWG) among week group 3 vaccinated pigs from vaccination to the end of the study and statistically significant increases in bodyweight and ADWG from inclusion to 10 weeks of age in week group 2 vaccinated piglets. However, no differences were noted in week group 1 presumably because more than 30 % of the vaccinated pigs were viremic at the time of vaccination. Furthermore, the proportion of pigs showing any abnormal clinical sign at least once at any of the examination time points was lower in vaccinated pigs than in control pigs. Based on the viremia results (qPCR), early onset of PRRS was detected in this herd. Viremia occurred at the time of vaccination in week group 1 and shortly after vaccination in week groups 2 and 3. Peak wild type PRRSV infection was assumed at 4 weeks post vaccination in all groups based on the number of PRRS positive pigs in the control groups. CONCLUSION: This study establishes that vaccination of piglets with Ingelvac PRRSFLEX® EU at 4 weeks of age improves weight gain and reduces the appearance of clinical sings during the growing period, even when the piglets are infected shortly after vaccination.