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The infertile mare
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Summary
It is particularly important to recognize and manage appropriately the mare which accumulates large volumes of fluid after breeding. In many cases, these mares are susceptible to postbreeding endometritis even though they have never been bred before. Often, sport or warmblood mares may not be presented to be bred until they are in their teens, and these older mares can be difficult to get pregnant.
Many of these mares have some common characteristics that resemble a syndrome. Endometrial biopsy samples reveal glandular degenerative changes and stromal fibrosis (endometrosis) as an inevitable consequence of aging, despite the fact these mares have not been bred. Another of the most common characteristics of these mares is the presence of uterine fluid. Often, an older maiden mare has an abnormally tight cervix, which fails to relax properly during estrus so that fluid is unable to drain and accumulates in the uterine lumen. In many cases, this fluid is negative for bacterial growth and presence of neutrophils. Once the mare is bred, the fluid accumulation is aggravated because of poor lymphatic drainage and impaired myometrial contraction compounded by the tight cervix. The amount of intrauterine fluid varies in individual mares, ranging from a few milliliters to more than a liter in extreme cases.
To maximize the fertility of these mares, it is vital that the veterinarian be aware of the possibility of this type of uterine and cervical condition. All too often owners assume that the fertility of these mares is comparable to that of young maiden mares; one of the most important aspects of breeding the old maiden mare is to make the owner aware that there is an increased possibility that she will be a problem. These mares must be considered highly susceptible and managed accordingly.
Management protocol for the mare with persistent fluid accumulation
These mares should be managed using the following protocol. Overall management of such mares must be excellent before breeding.
Hygiene
Good hygiene at foaling is essential, and all mares should be thoroughly examined post partum for the presence of trauma that might compromise the physical barriers to uterine contamination. Gynecologic examinations, particularly of the vagina, should be performed as aseptically as possible. Thorough digital examination of the cervix can identify fibrosis, lacerations, or adhesions that may need treatment before breeding. Because air in the vagina can cause irritation of the mucosa, it should be expelled by applying downward pressure with the hand through the rectal wall. Attention to hygiene at mating by using a tail bandage and washing the mare's vulva and perineal area with clean water (ideally from a spray nozzle that avoids the need for buckets) is important.
Correction of any external conformation defects
The mare should be evaluated for any conformational defects, and such defects should be corrected.
Correct timing of breeding
Breeding should occur at the optimal time and the number of breedings should be minimized. This means that these mares need very close monitoring of the estrous period by rectal palpation and ultrasonography. Prediction of ovulation is made easier by not breeding these mares too early in the year, before they have begun to cycle regularly. The use of ovulation induction agents is strongly recommended in such mares in an attempt to ensure they are only bred once. If feasible, the use of artificial insemination with fresh semen can be helpful to reduce (but not eliminate) the inevitable postbreeding endometritis.
Ultrasound evaluation of the uterus
The uterus should be examined by ultrasound examination to detect intraluminal fluid, in addition to conventional endometrial cytologic and bacteriologic techniques, before mating. Even if cytologic and bacteriologic studies have yielded negative results before breeding, older maiden mares usually accumulate fluid in the uterine lumen for more than 12 hours after mating. Ultrasound examination of the uterus 3 to 12 hours after mating is performed to assess the amount and echogenicity of any intrauterine fluid. This examination of mares and treatment given very soon after mating, before the bacteria have been long in a logarithmic growth phase, are important for the susceptible mare.
Before breeding
Work has shown that, although initially sterile and free of neutrophils, mares with uterine fluid accumulation before mating have a reduced pregnancy rate when no treatment is performed.
After breeding
Mares which have a history of fluid accumulation should have a large-volume uterine lavage performed four hours after breeding. The process is usually combined with oxytocin injection. Oxytocin remains the drug of choice in mares that accumulate free intraluminal uterine fluid and is my "first choice" uterotonic drug.
When the cervix fails to relax adequately, digital dilation of the cervix, with scrupulous attention to cleanliness, should be performed. This is one reason for ideally giving treatment to the susceptible mare before ovulation; a second reason is that oxytocin is less effective at increasing uterine pressure once the mare has ovulated.
After 20 minutes, the mare should be reexamined and any fluid pooling in the vagina removed. This is followed by infusion of a low volume of water-soluble, broad-spectrum antibiotic.
Further doses of oxytocin are given every four to six hours by the stud farm personnel.
In these mares which have failed to drain fluid with ‘normal’ treatments, systemic administration of antibiotics may be useful. The antigenic nature of spermatozoa in the uterus is well established and the post-breeding reaction is inflammatory in nature making it logical that corticosteroids may play a role in modulating the response.
The mare is re-examined the following day and oxytocin treatment repeated if fluid is still present. Only rarely will a second infusion of antibiotics or lavage procedure be performed due to the risk of uterine contamination. The day after mating is a crucial time to assess all mares, but too many clinicians fail to perform postbreeding evaluation of the uterus. Another important concept is to treat in relation to breeding and not wait for ovulation.
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