Figure 3.

Effect of dietary soybean meal (SBM; panel a) and phytase (panel b) on oral viral load of nursery pigs obtained from a porcine reproductive and respiratory syndrome (PRRS)–positive sow farm. Viral load was determined using real-time quantitative reverse-transcription PCR. Viral load is expressed as cycle threshold (Ct) values, defined as the number of cycles required for the fluorescent signal to exceed a threshold. Cycle threshold values are inversely related to the amount of viral RNA detected in the sample. Cycle threshold values of 36 and above suggest that saliva samples were PRRS negative and values of 35 and lower suggest that saliva samples were PRRS positive (Kleiboeker et al., 2005). Interactions of SBM × phytase × day, P = 0.41, and SBM × phytase, P = 0.11. Main effect of day, P = 0.09.