PCR
PCR was performed with DNA isolated from the blood, grass hay, and maize silage samples using EconoTaq PLUS  (Lucigen, WI, USA) and the OaPV primers (see Table 1) according to the manufacturer’s instructions. Conditions for PCR were as follows: 94°C for 2 min; 35 cycles at 94°C for 30 s, 58°C for 30 s, and 72°C for 20s; final extension at 72°C for 5 min. All the amplicons were sequenced.