Daily egg production rate and the aMPV antibody levels of naturally infected and inoculated ducks. Daily egg production rate represented by different flocks from three infected duck farms (A-Farm 1-F1&F2, Farm 2-F1&F2, Farm 3-F1&F2), two normal flocks from Farm 4 were used as the control (A-Farm 4-F1&F2). aMPV-antibody titer represented by three groups of ducks naturally infected and recovered (B - Naturally infected Flock 1, 2, 3), ducks in the normal flocks were used as the control (B - Normal Flock). S-01 was used to reproduce the disease. Ducks in group 1, 2 and 3 were inoculated with F1-, F5-, F10-embryo-passaged S-01 virus, respectively. Daily egg production rate (C) and aMPV antibody titer (D) are represented by three infected-duck groups and two control groups (Normal saline group, Control group). Statistical significance for an effect upon aMPV-C infection was determined using the Student’s t-test. Asterisks indicate statistical differences between control and aMPV-C groups (**P < 0.01; *P > 0.05).