The objective was to evaluate the effects of porcine respiratory and reproductive syndrome virus (PRRSV) infection and dietary soy isoflavone supplementation on carcass cutability and meat quality of commercial pigs. Barrows were randomly allotted to experimental treatments that were maintained throughout the study: non-infected pigs received an isoflavone-devoid control diet (NC, n = 22), and infected pigs received either the control diet (PC, n = 20) or that supplemented with total ISF in excess of 1,600 mg/kg (ISF, n = 25).

Following a 7-d adaptation, weanling pigs were inoculated intranasally with either a sham-control (PBS) or live PRRSV (1×105 TCID50/mL, strain NADC20). At 1 d postmortem (192–194 days of age; approximately 120kg BW), left sides were separated between the 10th and 11th rib for determination of loin eye area (LEA), backfat thickness (BF), and loin quality (ultimate pH, instrumental color, drip loss, visual color, marbling, and firmness). Loin chops were aged 14 d postmortem prior to Warner-Bratzler shear force (WBSF) determination. Belly width, length, thickness, and flop distance were determined. Data were analyzed as a one-way ANOVA with a model including effects of PRRSV status and dietary treatment, and also with single-df pre-determined contrasts to compare NC and PC (infection status) and PC and ISF (ISF effect within infected pigs). Carcass yield, LEA, BF, and estimated lean percentage did not differ (P > 0.26) among treatments. Loins from NC pigs had increased ultimate pH (P = 0.01), reduced L* scores (P = 0.005) coupled with darker visual color scores (P = 0.004), were firmer (P < 0.0001), and reduced drip loss (P = 0.01) compared with PC and ISF pigs. However, WBSF did not differ (P = 0.51) among treatments after 14 d of aging. Bellies from NC pigs were more firm compared with bellies from PC and ISF pigs (P < 0.01).