Sensitivity of the mPCR method. Three constructed plasmids (pMD-A, pMD-B, and pMD-J) and the three mixed plasmids (pMD-A/pMD-B/pMD-J) were diluted from 1010 to 101 DNA copies/μl to evaluate the sensitivity of the mPCR method. Shown are the sensitivity of pMD-A for ALV-A (A), the sensitivity of pMD-B for ALV-B (B), the sensitivity of pMD-J for ALV-J (C), and the sensitivity of pMD-A/pMD-B/pMD-J for ALV-A/B/J (D). M, DL2000 marker (TaKaRa, China).