Herd distribution of seropositive reagents to Chlamydia in Danish cattle.

19% of 733 cows and heifers in 25 Danish milking herds had CF antibodies against Chlamydia. The number of seropositive reagents in the individual herds varied from 0-45%. In one herd especially studied, the majority of reagents were among calves, while the number of reagents was reduced with increasing age, which indicated a coherence with enzootic pneumonia in calves. Apart from this and few cases of sporadic abortions, seropositive reactions could not be connected with any known chlamydial syndromes. A few old cows suffering from paresis puerperalis had titre increase or comparable high titres, indicating outbreak of a persistent infection. The demonstrated differences in serological results from individual herds and areas (Table II) may reflect a difference in the age of animals tested.