Effects of porcine reproductive and respiratory syndrome virus on pig growth, diet utilization efficiency, and gas release from stored manure

The objectives of this study were to examine the effects of porcine reproductive and respiratory syndrome virus (PRRSV) infection and vaccination on pig growth, dietary nutrient efficiency of utilization, manure output, and emissions of CO₂, CH₄, H₂S, N₂O, and NH3 gases from stored manure. Forty-eight pigs, aged 21 d at the start of the study, were subjected to 1 of 4 treatment combinations arranged in a 2 × 2 factorial design with main factors of PRRSV vaccination and PRRSV infection. Body weight, ADFI, manure output, and nutrient efficiency of utilization were assessed and gas emissions from stored manure were determined daily from 50 to 78 d of age and for 24 d after completion of the animal phase. Infection with PRRSV markedly reduced final BW, ADG, and ADFI (P < 0.01) and reduced efficiencies of ADF and ether extract utilization (P = 0.05 and P = 0.02, respectively) regardless of vaccination status. No significant treatment effects were found on manure output, manure pH, efficiencies of lignin utilization, and N retention. Infecting pigs with PRRSV increased daily manure CO₂ emission per pig (P = 0.01). There was an interaction between immunization and infection for N₂O per pig with manure from uninfected, vaccinated pigs producing as much as the manure from infected, vaccinated pigs whereas there was a difference by PRRSV infection state for nonvaccinated pigs. There were also interactions between treatments for H₂S and N₂O emissions per kilogram of manure volatile solids excreted (P = 0.01 and P = 0.0001, respectively) with the same pattern as for N₂O per pig; that is, the vaccinated pigs had similar rates of emission regardless of infection state. Pigs infected with PRRSV increased N₂O nitrogen per kilogram of total N excreted compared with noninfected groups (P = 0.03). Collectively, these results indicated that PRRSV infection caused decreased growth rates and nutrient utilization efficiency and increased gas emissions from stored manure.