Serum samples were collected from chickens of 53 layer flocks 40 to 500 days of age on 19 farms in Shimane Prefecture over a period from July to December, 1978. Antibodies against infectious bursal disease virus (IBDV) and
Mycoplasma synoviae (MS) were assayed on them by gel-precipitation and agglutination tests, respectively.
IBDV antibody was detected in 154 (30.6%) of 503 sera tested. The positive rate ranged from 0 to 100% among the flocks and from 3.3 to 49.5% in accordance with the advance in age. No IBDV antibody was detected on 2 of the 19 farms.
A total of 166 sera were selected from 30 flocks at random to include the same numbers of IBDV antibody positive and negative sera. When the positive rate of MS antigen was examined in them, it was 27.7%, varying from 0 to 73.3% with age. Positive sera were derived only from birds more than 101 days of age.
The MS antibody positive rate was about 2.7 times as high in the IBDV antibody positive sera as in the IBDV antibody negative sera.
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