Experimental infection of mares with Haemophilus equigenitalis.

Inoculation of Haemophilus equigenitalis into the uterus of 7 mares caused a disease clinically indistinguishable from contagious equine metritis. The duration of clinical signs varied from 4 to 11 days. The causative organism persisted for a relatively short time (2 to 10 weeks) in 5 mares, but in 2 others it established a carrier status and persisted until they were killed 6 and 10 months after infection. H. equigenitalis was recovered from the vestibule of the vagina and from a combined swab of the clitoral fossa and sinuses throughout the course of the infection. In some mares there were extended periods (2 weeks) when it could not be reisolated. All mares experienced a transitory serological response to infection. The complement fixation test was generally negative 12 weeks after infection whereas antibodies detected by the passive haemagglutination test and serum agglutination test were more persistent. In some animals the PHT and SAT titres increased during the breeding season following infection. The serological response did not appear to be related to the duration of infection.