Abstract: 【Objective】The objective of this study is to understand the process and regularities of ovarian lesions on ducks infected with duck Tembusu virus, and to provide data for the efficiency evaluation of vaccine using laying ducks ovary pathological inspection.【Method】Seventy 260-day-old laying cherry ducks were inoculated intramuscularly with duck Tembusu virus (HB strain) at dosage of 0.5ml(100 DID₅₀)/duck. Clinical symptoms were observed, and the egg production and feed intake were recorded daily. Serum samples were collected from all ducks for virus isolation via wing vein on 2 days post inoculation (dpi). Each serum sample was inoculated into five 6-day-old SPF chicken embryos via yolk-sac route at the inoculum of 0.1 ml per embryo. Then they were hatched at 37℃ further. The chicken embryos died in 24h were abandoned. The viral nucleic acid was detected by RT-PCR in the death chicken embryos during 24-72 h. If there were more than one (including one) death chicken embryos, and the nucleic acid testing was positive, then it was concluded that virus isolation was positive. On 4-10 dpi, 10 ducks were necropsied and the gross lesions of the reproductive system were observed every day. The pathologic rate was calculated, and the gross lesions of the reproductive system were conducted including whether there were eggs in the fallopian tube, whether the follicle was deformed, hemorrhaged or ruptured or not. According to the statistical pathologic rate, the time, the content of the examination and the criterions for determining lesion ovary were confirmed. 【Result】 (1) Feed intake and egg production decreased significantly on 3-6 dpi. The mental state of the duck on 7 dpi improved, and feed intake began to rise on 8 dpi. (2) Virus isolation of 70 ducks were all positive except one duck. The virus positive isolation rate was 98.6% (69/70) on 2 dpi. (3) On 4-10 dpi, a total of 64 laying duck reproductive organs can be determined. (4) On 4-10 dpi, the ovarian lesions rate were 66.7% (6/9), 100% (10/10), 100% (10/10), 100% (9/9), 100% (9/9), 100% (9/9) and 100% (8/8) respectively. (5) Eggs were found in fallopian tube of 2 ducks among 10 ducks that were necropsied on 4 dpi, and there was no egg found in fallopian tube of the remaining 62 ducks. The egg negative rate was 96.9(62/64). (6) On 4-10 dpi, the proportion of deformed follicular duck and hemorrhaged follicular duck were both 96.9% (62/64), and the proportion of deformed and hemorrhaged follicular duck was 95.3%（61/64）, while the proportion of ruptured follicular duck was 34.4% (22/64).【Conclusion】 (1) The time for the examination of the pathological changes of ovary was determined as 7 to 8 dpi. (2) The criterion of abnormal follicle is that one of the lesions of deformation and hemorrhage or both were found. The criterion of lesion ovary is that three abnormal follicles or more appeared and no egg in the fallopian tube.

Key words: duck tembusu virus disease, ovary, pathological change