Sampling of the surface of the endometrium for pathogenic microflora is an important part of the breeding soundness evaluation of the mare. Additionally, most breeding sheds and stallion owners require broodmares to have a negative uterine culture before natural mating. Breeds that allow artificial insemination may be less restrictive with this requirement. Other indications for endometrial culture include recent dystocia or retained fetal membranes, detection of intrauterine fluid by ultrasonography, or previously diagnosed endometritis.
It is imperative that any anatomic defects — such as poor perineal conformation, rectovaginal fistulas, perineal lacerations, and vesicovaginal reflux — be surgically corrected. Without doing so, endometritis will recur despite appropriate antimicrobial therapy. A list of agents used for intrauterine antimicrobial therapy in the mare is given in Table Antimicrobial Therapy for Intrauterine Use in the Mare. In most mares, a volume of 50 to 100 ml will give adequate dispersion over the entire endometrial surface. Mares whose uteri are enlarged may require volumes greater than 100 ml to achieve uniform distribution throughout both horns and the body of the uterus. Treatment once daily for 4 to 6 days during estrus is usually adequate for most cases of endometritis. It is often beneficial to precede antimicrobial infusion with uterine lavage, thereby mechanically removing organic debris, which can interfere with the efficacy of most antibiotics. Postpartum mares — or those with an especially enlarged uterus that lacks tone — benefit temporarily from lavage with warm saline before infusion with antimicrobial agents. Oxytocin is an effective tool to enhance uterine clearance of the mare. It is advisable to wait several hours after using any intrauterine antimicrobial agents before administering oxytocin; otherwise, uterine contractions will prematurely expel the antimicrobial agent. In such cases, combining uterine lavage and oxytocin with systemic antimicrobial therapy may prove more efficacious and cost-effective.
Table Antimicrobial Therapy for Intrauterine Use in the Mare*
|amikacin sulfate||2g||Gram-negative organisms; buffer with equal volume 7.5% bicarbonate|
|ceftiofur||ig||Broad spectrum (Streptococcus zooepidemicus)|
|gentamicin||1-2 g||Cram-negative organ-|
|sulfate||isms; buffer with equal volume 7.5% bicarbonate|
|kanamycin sulfate||1-2 g||Escherichia coli; toxic to spermatozoa|
|penicillin||5 million units||S. zooepidemicus|
|polymixin B||1 million units||Pseudomonas spp.|
|ticarcillin/ clavulanic acid||6 g/200 mg||Broad spectrum|
|nystatin||500,000 units||Antimycotic; must use sterile water (precipitates in saline)|
|clotrimazole||500 mg||Antimycotic; suspension or cream; q24-48h for 1 -2 weeks|
|vinegar||2%||Antimycotic; 20 ml wine vinegar in 1 L of saline; used as a lavage fluid|
*Parts of this table from Asbury AC, Lyle SK: Infectious causes of infertility.
The use of systemic antimicrobial therapy is becoming an increasingly popular route for treating mares with endometritis, especially in mares prone to postmating endometritis during the postovulatory period, in mares whose biopsy shows evidence of inflammation deep in the stratum spongiosum, and in mares that receive embryos by transcervical transfer. Trimethoprim/sulfa combinations (30 mg/kg q24h or divided ql2h PO) and ceftiofur (4 mg/kg IM q24h) are broad-spectrum antibiotics that should be safe for the early embryo. Enrofloxacin (7.5 mg/kg q24h PO) also has broad-spectrum activity but would not be recommended for use in pregnant or potentially pregnant mares. The bioavailability of the tablet form of enrofloxacin appears to be superior to that of the injectable preparation.
Uterine infections due to fungal or yeast infections are difficult to treat and often follow chronic bacterial endometritis with extensive intrauterine antibiotic use. Clotrimazole and uterine lavage with dilute vinegar solutions are anecdotally the most effective treatments but can require more than one course of therapy. Dilute povidone-iodine lavage solutions (0.05%) have also been suggested. Vaginal speculum examinations are important to monitor cervical inflammation. Some mares are extremely sensitive to even dilute iodine solutions, in which case severe cervicitis, vaginitis, and intraluminal uterine adhesions can result. Occasionally spontaneous recovery from fungal endometritis is seen. In most cases these infections tend to be extremely difficult to resolve; the owner should be given a guarded prognosis for fertility.