The experimental infection of ponies with contagious equine metritis.

This study focused on understanding the infection process and consequences of contagious equine metritis (CEM), a bacterial disease affecting horses, in pony mares and stallions. The results showed various responses to the infection, with some animals exhibiting symptoms and others becoming asymptomatic carriers.

Experiment on Pony Mares

• In the study, four pony mares were infected with contagious equine metritis through intracervical inoculation, a process of injecting the bacteria directly into the cervix. One mare was infected through coitus with an infected stallion.
• The infected mares developed acute endometritis, an inflammation of the inner lining of the uterus, along with destruction of the endometrial epithelium, the layer of cells that lines the uterus.
• Two of the infected mares seemed to spontaneously eliminate the infection from their genital tracts within 3 to 4 weeks, suggesting the body was able to clear the infection without specific medical treatment.
• However, a third mare remained infected over a long period with the bacteria persisting in the clitoral fossa, a depression near the clitoris. This mare showed no symptoms, qualifying as a symptomless carrier of the infection.

Experiment on Pony Stallions

• Four pony stallions were likewise infected, specifically in the urethral fossa, another depression this time situated near the urethra, of the external male genitalia.
• The infected stallions did not present any signs of infection while the bacterium remained in their systems for varied durations.
• Two of the stallions seemed to spontaneously eliminate the bacteria as well.
• An infected stallion was able to transmit the bacteria to a healthy female through coitus, indicating that asymptomatic or symptomless carriers can still be infectious to others.
• The research also pointed out that bacteriological tests on infected stallions can sometimes yield false negatives, failing to reveal the presence of the disease in the external genitalia. Therefore, it was concluded that repeated tests are necessary before declaring a stallion free of infection.

The study underscores the complexities in the transmission and management of contagious equine metritis among horses, suggesting that monitoring and repeated testing are crucial given that the infection can exist without symptoms and yet still be contagious.