Effect of various stocking methods and extra-label PRRS vaccination on average daily gain
Steve A. Sornsen, DVM, MS; Jeff J. Zimmerman, DVM, PhD; Michael B. Roof, PhD
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Purpose: To evaluate the effect of three different methods tostock nurseries (from one source or two, over 24 hours or 5 days, with vaccinated or nonvaccinated pigs) on average daily gain (ADG) in commercial nurserypigs.
Methods: Three commercial nurseries were stocked over 3 consecutiveweeks with either: 5-day fill of pigs intranasally (IN) vaccinated againstPRRSV from a single source (the "vac-5" group); 5-day fill ofpigs from a single source that were unvaccinated (the "nonvac-5"group); and 24-hour fill of nonvaccinated pigs from two sources (the "nonvac-24"group). On day 0, pigs were penned according to entry weight. Eighteen pensof pigs, one pen per room, was weighed on day 0 and weekly thereafter. Thirtysix individual pigs were bled weekly and tested for antibodies against PRRSVand assayed for the presence of PRRSV in serum. Virus isolates were characterizedby the restriction fragment length polymorphism (RFLP) assay to determineif they were compatible with vaccine or with field virus.
Results: ADG did not differ significantly between the nonvac-24pigs and vac-5 pigs. However, pigs in both of these nurseries gained significantlyfaster (P<.05) than pigs in the nonvac-5 nursery. Nearly all ofthe monitored pigs (91 of 98) had seroconverted to PRRSV by the endof the trial, regardless of treatment. Vaccinates had a significantly higher(P<.0001) mean ELISA S:P ratio (3.71) than nonvaccinates (1.76)at the end of the trial. Nonvac-24 pigs had a significantly higher (P<.01)ELISA S:P ratio than either the vac-5 or the nonvac-5 pigs. On day 0, pigsin the nonvac-5 nursery had a positive ELISA S:P values, while the vac-5pigs had S:P values of 0.24 and nonvac-24 pigs had S:P values of 0.25. Isolatescompatible with vaccine virus or field virus (isolate ATCC VR2332) werefound in pigs in all three nurseries. Isolates with RFLP patterns differentfrom vaccine virus or isolate ATCC VR2332 were also found in all three nurseries.
Implications: Vaccinates performed better than nonvaccinates undera 5-day nursery fill system in this system. However, vaccinates under a5-day nursery fill system did not perform significantly better than nonvaccinatesunder a 24-hour nursery fill system.