The cow is extremely vulnerable to infection during this stressful period. When acute metritis is present, it usually subsides 2 to 3 weeks after the infection has been cleared. However, acute metritis may develop into a chronic condition, which persists for a longer period. Cause A large number of microorganisms have been implicated as causes of metritis. Bacteria, viruses, fungi and protozoa have been cultured from uteri when metritis has been present.
Microorganisms enter the uterus through several routes.
Most commonly organisms, particularly bacteria and fungi, contaminate the uterus during calving or the early postcalving period. The reproductive tract is very susceptible at this time, especially if trauma or lesions in the vagina or vulva are present, and the animal's natural defenses are lowered. Any assistance or manipulations performed during parturition can easily introduce organisms into the uterus. Infection can be transmitted either by an infected bull or carried by the bull to a susceptible female from an infected female. Semen-borne infections are less common types of infections.