from the Vet Corner Archives

Veterinary Corner 11/01: Postmating Uterine Infection in the Mare

by Frosty Franklin, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069

As a horse breeder, perhaps, you have not realized that every time a mare is bred she has a transitory and probably physiological uterine infection and inflammation (endometritis).

Research has revealed that semen and the microorganisms introduced to the reproductive tract by breeding are responsible for the inflammation. Fertilization occurs in the tiny duct (oviduct) next to the ovary. After fertilization has occurred the fertilized egg remains in the oviduct for 5 days. At day 6 the conceptus (maturing egg) descends into the uterine lumen. If the mare has not spontaneously cleared the infection and inflammation from the uterine lumen, embryo survival is unlikely. Inflammation of the uterine lining (endometrium) that is still present after the 6th day after ovulation will cause lysis of the corpus luteum (CL) on the ovary and the mare to return to estrus (heat) early.

Mares that can clear the uterus easily within a few hours are resistant mares (resistant to endometritis). Their natural defenses and clearance mechanisms are responsible for the rapid removal of microorganisms and inflammatory products within 24 hours. Susceptible mares (susceptible to endometritis) have a delayed and dysfunctional uterine clearance mechanism. These mares accumulate fluid within the uterus for numerous reasons: decreased smooth muscle activity of the uterus, poor conformation of the perineum and a long pendulous uterus hanging over the brim of the pelvis (common in older, multiple foaling mares) resulting in poor drainage from the cervix, decrease reabsorption of fluid by the lymphatic vessels and increase production of mucus and fluid by the glandular cells of the uterine lining.

Mares that are repeatedly bred to fertile stallions should be suspected of having postmating endometritis. A presumptive diagnosis is based on the mare's reproductive history, clinical signs, and the presence of intraluminal uterine fluid based on an ultrasonic evaluation more than 24 hours following breeding. A shortened estrous cycle following mating is suggestive of persistent postmating endometritis.

Before breeding the susceptible mare, the reproductive tract has to be free of predisposing factors and current infections. She may need surgery to correct conformation defects or treatment for an existing uterine problem. If she has been barren for 2 or more years, a uterine endometrial biopsy is highly recommended.

In my practice mares that are repeat breeders are examined at 20 hours postmating via transrectal ultrasound. They are evaluated for intraluminal uterine fluid and edema of the endometrium. Mares with an elevated edema score (or fluid within the uterus) are diagnosed as postmating endometritis.

Treatment should be aimed at limiting the exposure of the mare's reproductive tract to unnecessary breeding and assisting the mare in physically clearing the reproductive tract of fluids, inflammatory products, and microorganisms once mating has occurred.

I recommend mares be carefully teased and the reproductive tract ultrasounded frequently during estrus (heat) and bred only one time per heat cycle just before ovulation based on the ultrasonic image of the mature follicle. HCG, a hormone that aids ovulation and is helpful in timing breeding and ovulation, can be given. Oxytocin administered 4 to 8 hours postmating effectively clears the uterus. Oxytocin, a hormone, increases the smooth muscle activity of the uterus for approximately one hour. Uterine lavage or irrigation with large volumes of warm Ringers or buffered saline solution effectively removes larger volumes of fluid and inflammatory products from the uterine lumen. Many equine practitioners use oxytocin and uterine lavage in combination. Buffered antibiotic solutions can be infused into the uterine lumen to remove the microorganisms attached to the uterine lining. Research indicates that treatment after each breeding more effectively aids the mare in clearing fluid accumulations within the uterus.

Mares that are repeat breeders and mares that are barren can be difficult to manage. They are time consuming and expensive. To successfully manage them, one needs a diagnosis of their problems. The time is now. Your veterinarian can help with uterine biopsy, conformation evaluation, gynecologic exam or reproductive tract surgery, such as a simple Caslick's procedure that can eliminate wind sucking and vaginal contamination and have the mare ready to breed this spring.

Frosty Franklin


Previous Issue:
November 2001

Wishing Star
Results Issue

Wishing Star
Gllop 2001

Ceremony at the 2001 Wishing Star Gallop

Conculsion Tops Wishing Star
Gallop's Sale

Baxter Black -
The Environmental Inspector

Weaver Quarter Horse Annual Production Sale Results

Vet Corner -
Post Mating
Uterine Infection
in the Mare

REAL ESTATE SECTION - Rehabilitation
of Old Barns

November 3, 2001 3:41 PM