Effect of PRRS vaccination on average daily gain: A comparison of intranasal and intranasal-intramuscular administration
Steve A. Sornsen, DVM, MS; Jeff J. Zimmerman, DVM, PhD; Dale D. Polson, DVM, PhD; Michael B. Roof, PhD
Complete article is available online.
PDF version is available online.
Purpose: To evaluate the effects of two extra-label vaccination(RespPRRS(R), NOBL Laboratories, Inc.) procedures against porcine reproductiveand respiratory syndrome (PRRS) on average daily gain (ADG) in a commercialoffsite nursery.
Methods: Neonatal pigs were assigned to one of three treatmentgroups at each of 10 offsite sow farms, so that all pigs born in each ofthree rows of crates in the farrowing room received the same treatment.One group (controls) received no vaccine (n 5400 pigs); a secondgroup received 1 mL PRRS vaccine intranasally (IN) at 5-7 days of age (n5400 pigs); a third group received 1 mL PRRS vaccine IN at 5-7 days of ageplus a second 1-mL dose intramuscularly (IM) just prior to weaning at approximately17 days of age (n 5400). At weaning, pigs were moved to an offsite nursery,where they were sorted by entry weight (small, medium, and large) and treatmentgroup, and placed in pens of 22 pigs each. Nine pens per room were randomlyselected to be monitored in the study; one pen from each treatment and sizegroup. Weight gains were recorded weekly for each pen of pigs and individuallyfor one ear-tagged pig per pen. Serum samples were collected from all taggedpigs on days 0, 28, and 49 and assayed for antibodies (ELISA) and virus.All viruses isolated were characterized by restriction fragment length polymorphism(RFLP). A total of 51 pigs and pens were included in each treatment group.Seventeen rooms were selected for the study for a total of 153 pigs andpens.
Results: No significant differences in weight gains were observedamong the treatment groups (P =.49), indicating that vaccinated pigsperformed no better than nonvaccinated pigs. Nor did route of administration(IN versus IN/IM) have an effect on ADG in this study. Pigs with largerentry weight gained significantly faster than smaller pigs (P <.0001). There was no significant interaction between treatment and entrysize in this trial (P = .24). Nearly all pigs seroconverted to PRRSV,including the nonvaccinated control pigs. Viruses whose RFLP profile wascompatible with RespPRRS(R)/2332 virus were isolated from nonvaccinatedcontrol pigs, as well as vaccinated pigs. Viruses whose RFLP profile wasnot compatible with RespPRRS(R)/2332 virus were also found in both vaccinatesand nonvaccinates. Thus, differentiation of viruses indicated a probablespread of vaccine virus from vaccinated pigs to nonvaccinated pigs withconcurrent circulation of field virus in both groups.
Implications: In this commercial production system, vaccinationwith a PRRSV vaccine was not observed to have an effect on ADG using eitherof two extra-label protocols. Nonvaccinated pigs housed in proximity tovaccinated pigs became infected with vaccine virus.