Abstract: Major viral infectious agents that caused reductions in egg-laying ducks were targeted for this study. A clinical sample collection on infected egg-laying ducks at different growing stages from a number of provinces in the nation, as well as an analysis on the samples using the reverse transcription polymerase chain reaction (RT-PCR), was conducted from 2011 to 2015. The samples from the ducks that showed a reduction on egg-laying were positively contaminated with avian influenza viruses (AIV) at a rate of 25.1% (212/843), with duck Tembusu virus (DTV) at a rate of 27.7% (298/1076), with avian paramyxovirus type 1 at a rate of 9.3% (46/495), and with duck enteritis virus at a rate of 1.3% (8/614). DTV infection in Sheldrake ducks at pre-egg-laying stage showed a positive rate of up to 40.8%, with a peak positive rate of 70.5% in 2015. Thus, DTV and AIV were seen as the crucial infectious agents that posted heavy threat to the duck farming in China. DTV is not only harmful in causing drastic reduction in egg production of mature ducks, but also in infecting the growing, pre-egg-laying ducks. Consequently, measures to curb and prevent wide spread of Tembusu viral disease was deemed an urgent task for the duck egg industry.

Key words: egg-laying duck, growing-period laying duck, major viral infection, detection