Experimental infection of the pregnant cow with Chlamydia psittaci

: Seven cows were inoculated with two strains of C. psittaci from bovine origin. Their chlamydial excretion, complement fixing (CF) antibody titer and hormonal pattern, at calving or abortion were monitored. Five of the six pregnant inoculated cows had a pathological parturition, and a CF antibody titer greater than 40 during more than two months post-abortion. Three of them excreted Chlamydiae at calving. The other inoculated pregnant cow, the inoculated non pregnant cow and the three contacts had CF titer less than 40 during the same period. The progesteronemy and the oestradiol 17 beta level of the two early aborted cows were abnormal.