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Treatment options for subfertile mares (Proceedings)


There are probably as many opinions as there are veterinarians in what constitutes an appropriate set of diagnostic procedures and therapeutic options for a subfertile or problem mare.

There are probably as many opinions as there are veterinarians in what constitutes an appropriate set of diagnostic procedures and therapeutic options for a subfertile or problem mare. This summary will describe the routine procedures that are performed in my practice and some of the most basic treatment protocols. It is emphasized that although some blanket therapies are established for certain routine conditions, the daily examination as well as the clinical signs will dictate changes or adjustments to the treatment protocol.


It is well established that a high percentage of mares that do not become pregnant have some degree of uterine contamination. It must be assumed that the uterine environment is a sterile environment that should be free of inflammatory cells. In a recent study by Riddle et al in 2006 it was reported that mares with bacterial uterine growth and/or cytological evidence of inflammation had a reduced pregnancy rate. In my practice, uterine culture and cytological evaluation of the uterus is the first diagnostic procedure that is performed. Case selection for performing a culture and cytological evaluation include: i) Mares that ovulate with a high degree of edema, ii) Mares that have free uterine fluid that is present throughout the estrus period, iii) Mares with short or long luteal phases, iv) Mares that have failed to conceive after being bred under good breeding management conditions with a stallion of good fertility v) Mares with evidence of uterine or vulvar discharge.

Mares that have a positive culture (isolation of micro-organisms) or a positive cytology (greater than 2 neutrophils/field) when appropriate techniques are used, should be treated. Appropriate techniques include but are not limited to taking the swabs when there is uterine edema and/or free uterine fluid, clean aseptic techniques and proper time of contact between swab and endometrial surface. When swabs are negative and an infection is suspected, a uterine biopsy specimen is submitted for culture or a low volume uterine flush is performed and a swab submitted from that specimen.

The cervix must be examined carefully to ensure that it is patent. Endoscopic evaluation of the uterus may be performed to determine if there are adhesions or foreign material.

Treating and breeding a problem mare

In order to establish an appropriate therapy in addition to an uterine culture and cytology, the degree of uterine edema and the presence or absence of uterine fluid is evaluated. If fluid is present the relative amount should be recorded, as should the degree of cervical relaxation and stage of the cycle. For example, a mare with heavy uterine edema and no follicles should be considered abnormal, while a mare with a large preovulatory follicle and no edema and a tight cervix could be in diestrus.

Treatment for bacterial uterine infections

There is no standard or blanket therapies in my practice and all mares are treated based on clinical signs. In order to minimize the interval from treatment to breeding it is critical that the previous ovulation date is accurately recorded in order to short cycle the mare with prostaglandin after treatment.

Mares with bacterial growth from uterine culture will be infused daily for 3 to 5 days with an appropriate antibiotic in a volume not to exceed 50 mls. A rectal ultrasonographic exam is performed daily in treated mares to evaluate the amount of uterine fluid accumulation. If fluid accumulation is detected either before the first intra-uterine infusion or during the treatment period a uterine lavage consisting of lactated ringers is performed. All efforts are made to recover the uterine lavage fluid. In an effort to maintain the uterus free of fluid, mares that are infused with intra-uterine antibiotics are administered carbetocin or oxytocin respectively two to four times daily. This is particularly important in those mare that fail to relax or open the cervix completely. Every effort is made to treat mares during the follicular phase of the cycle so that cervical relaxation, white blood cell influx and uterine contractility can assist in uterine evacuation. Antibiotics are given systemically to mares when the bacteria recovered is resistant to antibiotics that can be safely infused into the uterus, (i.e. enrofloxacin). Systemic antibiotics may also be used in mares with poor perineal conformation that require a constant vulvar seal maintained by the vulvoplasty (Caslick), and in mares with a pendulous, dependent uterus that does not drain fluid readily.

The degree of uterine edema is monitored daily by ultrasonography. Mares that ovulate with a high degree of edema or with edema that persists for more than 24 hrs post ovulation are considered abnormal. An endometrial biopsy sample is taken from mares with abnormal uterine edema to determine the degree of uterine inflammation if they are to be bred with expensive frozen semen.

Mares treated for endometritis are usually bred on the prostaglandin induced cycle after the treatment period without obtaining a second uterine culture. However these mares are treated examined 4-12 hrs after insemination and uterine lavage and ecbolic agents are used after breeding.

Mares considered to be problem breeders are only inseminated once preferably with good quality semen. Mares bred with fresh semen are mated in the 48 hrs before ovulation, within 24 of being bred with cooled semen and within the 4 hr interval after ovulation with frozen semen. Frozen semen is deposited at the tip of the uterine horn ipsilateral to the dominant follicle by rectally guided insemination. Cooled semen of mediocre quality is centrifuged and the mare inseminated with 2-2.5 mls of centrifuged semen also deposited by deep horn insemination. To insure ovulation, mares are given an ovulatory inducing agent. All mares are evaluated between 4 and 8 hrs post insemination to evaluate the amount of fluid accumulation and degree of edema. If free fluid is detected a uterine lavage is performed using warm ringers lactate until the efflux is clear. Uterine lavage is performed regardless of the ovulation status. Waiting for the mare to ovulate, may result in a prolonged uterine inflammatory process that could be difficult to control particularly if the mare is bred 24-48 hrs prior to ovulation. If no fluid is detected but the degree of uterine edema has increased the mare is treated with 20 mgs of Dexamethasone IM, and an ecbolic agent such as oxytocin, carbetocin is used for no more than 3 consecutive days. Mares are examined on a daily basis thereafter in order to establish day of ovulation and to evaluate uterine contents and edema pattern. A Caslick's procedure is performed on most problem mares since not all mares need to have a sloped vulva to aspirate air or become contaminated with fecal material. Many mares with a small ano-genital distance (anus to dorsal vulvar commissure) are easily contaminated.

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