Serological observations on Chlamydia psittaci infection in Finnish dairy herds.

Chlamydial complement fixing antibodies were followed in 5 small Finnish dairy herds. All 53 animals in the herds were bled. In herds A, B, C and D the blood samples were collected in May and in the following autumn after the pasturing period and in herd E over a period of 2 years at about 1 ½-month intervals. The frequencies of positive reactions among the adults and the calves younger than 1 year did not differ significantly from each other, but there were considerable seasonal variations in the frequencies. The highest frequency was found during springtime and early summer and the lowest in autumn.