Several specific diseases are associated with metritis or endometritis. These include brucellosis (see Brucellosis in Large Animals), leptospirosis (see Leptospirosis), campylobacteriosis (see Bovine Genital Campylobacteriosis), and trichomoniasis (see Trichomoniasis). More often, endometritis is the result of nonspecific infections.
The normal uterus is a sterile environment, in contrast to the vagina, which hosts numerous microorganisms. Opportunistic pathogens from the normal vaginal flora or from the environment may invade the uterus from time to time. A healthy uterus is able to rid itself of these transient infections very efficiently; however, in the immediate postpartum period, the uterus of cows is usually contaminated with a variety of organisms. Within days or weeks postpartum, the sterile uterine environment is reestablished in most animals. In those in which infection persists, chronic or subacute endometritis develops and has a detrimental effect on fertility. The prevalence of subclinical endometrial inflammation in dairy cows seems to exceed the prevalence of uterine infection. The pathogenesis of this form of endometritis is not yet understood, but it is becoming increasingly clear that postpartum uterine diseases, particularly in high-producing dairy cows, are mediated by impaired immune response, probably related to negative energy balance.
In cows, the causative organisms are most often Trueperella pyogenes, alone or in association with Fusobacterium necrophorum or other gram-negative anaerobic organisms. Signs of infection vary from obvious and persistent purulent exudate from the uterus to inapparent infection. Changes in uterine consistency may occur, but transrectal palpation alone is an insensitive means of diagnosis. The presence of purulent exudate in the vagina does not necessarily confirm endometritis; the source of the exudate may be the cervix or, occasionally, the vagina itself. Manual vaginal examination or use of a device to recover vaginal content may also allow evaluation of vaginal exudates for diagnosis of clinical endometritis. Diagnosis of subclinical (cytologic) endometritis requires use of endometrial cytology, ultrasonography, or endometrial biopsy, because other signs are often absent. Cows with endometritis do not exhibit any systemic signs of illness, and appetite and milk production are usually unimpaired.
For decades, endometritis in cows has been treated with intrauterine infusion. Although infusion of antimicrobials may rid the uterus of bacteria, there is little evidence that it eliminates the endometrial inflammation or restores fertility. Many preparations routinely administered into the bovine uterus are detrimental to uterine tissue. Increased concern about milk and carcass residues, along with poor or uncertain results, should discourage intrauterine therapy as a routine approach to management of bovine endometritis. Intrauterine infusion of cephapirin in a form specially formulated for intrauterine use, and available in many countries (but not the USA), has enhanced fertility in dairy cows with endometritis. Systemic use of antimicrobials for treatment of clinical or subclinical endometritis has not been evaluated.
Cows are more resistant to uterine infection during estrus, and as cows undergo more estrous cycles after parturition, the prevalence of endometritis diminishes. This has led to increased use of prostaglandin F2α or its analogues, at usual luteolytic doses, for the management of endometritis, although there is little evidence that such use reduces the incidence or effect of endometritis.
Although profound endometritis accompanies contagious equine metritis (see Contagious Equine Metritis) in mares, most breeding problems are related to endometritis caused by nonspecific infections. In mares, the most common etiologic agent of endometritis is Streptococcus zooepidemicus, but several other organisms may be involved, including Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Yeasts and fungi are incriminated in some cases, particularly in mares with reduced resistance, or as a sequela of exuberant antimicrobial therapy.
Visible exudate is rarely a feature of endometritis in mares. (Contagious equine metritis is a notable exception.) Endometrial inflammation is best confirmed by examination of endometrial cytology or biopsy samples. Additional support of the diagnosis is provided by ultrasonographic demonstration of intraluminal free fluid, especially during diestrus, or by isolation of potentially pathogenic bacteria from appropriately guarded swabs of the endometrium. Because most causative organisms are common commensals, isolation of bacteria alone is not sufficient evidence for diagnosis. Nevertheless, evidence suggests that fertility of mares is impaired if either endometrial cytology or culture is positive.
Intrauterine therapy is still commonly used in mares. Many antimicrobial drugs have been used, and effective doses determined mainly empirically. Some examples include penicillin (5 million U; effective mainly against S zooepidemicus), ticarcillin (6 g; broad spectrum), ampicillin (3 g of soluble preparation), gentamicin (2 g, buffered with bicarbonate; effective especially against gram-negative agents), and kanamycin (2 g; effective against gram-negative bacteria). For fungal or yeast infections, 100 mg of amphotericin B or 500 mg of clotrimazole have been effective. Treatment should be continued for several consecutive days, preferably during estrus. Most of the above treatments constitute extra-label drug use in the USA.
Some mares appear particularly susceptible to postbreeding endometritis. These mares accumulate fluid in the uterine lumen after mating or insemination. This is related to persistent endometrial inflammation. In contrast, normal mares have a vigorous, but transient, inflammatory response to mating, and the uterus rapidly regains its sterile, noninflamed status. Postbreeding endometritis may be treated by uterine lavage or by use of oxytocic drugs to rid the uterus of fluid.
A form of endometritis characterized by profuse vaginal discharge at the onset of estrus has been described in Europe and other regions. The causative agent is usually Staphylococcus hyicus or E coli, and the disease seems to be transmitted at mating or artificial insemination; signs are seen 15–25 days later during the subsequent proestrus or estrus. Infection may be of long duration, with signs recurring at each estrus. Some sows recover spontaneously, but there does not seem to be any effective treatment for those that do not. At necropsy, copious quantities of purulent exudate may be found in the uterus, making this condition more akin to pyometra (see Pyometra in Large Animals).
Endometritis has been seen in sheep, goats, and camelids. In commercial sheep and goat flocks, diagnosis is seldom made antemortem, and treatment is generally impractical. In animals with a persistent uterine discharge, remnants of a macerated fetus should be considered as a nidus of chronic infection. Endometritis in camelids is usually treated empirically based on treatments for cattle and horses.