Association of PRRSV-JA142 viral loads with the growth rate of pigs. A The viral loads in sera obtained from negative control (NC) and infected (I) pigs at 0, 3, 7, 10, 14, 21, 28 and 28 dpc were quantified by real-time reverse transcription-PCR. The viral titres were calculated based on the standard curve of the threshold cycle number plotted against the known virus titre. B The residual viral lung loads at each necropsy day were quantified using MARC-145 cells based on a microtitration infectivity assay. C The body weight of the euthanized pigs was measured at −3, 3, 10, 21, 28 and 35 dpc, and the average daily weight gain (ADWG) was calculated. D The correlation between viremia and ADWG was tested during the course of infection. The bars represent the means, and the error bars represent the standard errors of the mean (SEM). Bars showing asterisks (*) represent values that differ significantly from each other (** indicates p ≤ 0.01 and *** indicates p ≤ 0.001).