How to breed the highly susceptible mare in practice

How to breed the highly susceptible mare in practice

This will focus on a personal approach to the practical problem of management of the highly susceptible mare which the author has found to work well in daily veterinary practice The objective of the veterinarian and breeding farm owner/ manager should be to produce the maximum number of live, healthy foals from mares bred during the previous season. We could add 'as early as possible' to this in many breeding programs. One of the main obstacles to this goal is the mare which is susceptible to recurrent acute endometritis following breeding.

Management of the Susceptible Mare

Ultrasound evaluation of the uterus for the detection of intraluminaluterine fluid is very useful.

Recent work has shown that, although initially sterile and free of neutrophils, mares with uterine fluid accumulation before breeding have a reduced pregnancy rate when no treatment is performed (Pycock and Newcombe 1996).The amount of fluid which should be considered significant is not clear and it may be that quantity is more important than nature. This is particularly true of fluid appearing during estrus. The significance depends to some extent on when during estrus the fluid is observed: fluid detected early in estrus may have disappeared when the mare is further advanced in estrus and the cervix relaxes more. Generally if there is more than half an inch of fluid during estrus some attempt should be made to remove this prior to breeding using oxytocin. If the volume is above one inch, the fluid may need to be drained and investigated for the presence of inflammatory cells and bacteria. The mare may then need to have a large-volume uterine lavage. Fluid indiestrus is more serious and any detectable volume nearly always indicates a problem. Recognition of the importance of the mechanical evacuation of uterine contents accounted for the relatively recent introduction of large-volume uterine lavage as a treatment for inflammatory disorders of the mare's uterus. I have found this to be a useful therapeutic protocol in many cases. The technique involves the mechanical suction or siphonage of 2 to 3litres of previously warmed saline infused into the uterus via a catheter that has been retained within the cervix via a cuff. The most convenient is a large-bore (30 French, 80 cm) equine embryo flushing catheter.

Undoubtedly large volume lavage is beneficial in many cases, particularly the mare with a relatively large (above one inch depth) accumulation of fluid after breeding.

For optimal practical management, the ideal method of treatment will involve the use of a non-invasive technique with early and complete elimination of any intrauterine fluid. This can be performed more realistically in practice when it may be difficult to justify the time needed to large-volume lavage the uterus. I have found the following management protocol to be useful in the highly susceptible mare (i.e. a mare which from past experience/history is known to produce a large amount (several inches depth) of luminal fluid after breeding). It should be remembered that this approach is being suggested as part of the management of the susceptible mare and is not suggested as a routine for all mares.


The protocol for management of the highly susceptible mare is as follows:

A single breeding must be arranged 1-2 days before the anticipated time of ovulation. This early breeding allows more time for drainage of fluid via an openestrous cervix and also utilises the natural resistance of the tract to inflammation during estrus. In the author's opinion, treatment for endometritis is ideally performed on the day before, or the day of, ovulation.It is my opinion that it is better to treat in relation to breeding and not wait for ovulation. This represents a new approach for many practitioners. Progesterone concentrations rise rapidly in the mare and any post-ovulation treatment has an increased risk of uterine contamination. In addition, uterine fluid is less likely to drain if the cervix is beginning to close.

Ultrasound examination of the uterus 3-12 hours after breeding. The aim is to assess the amount and echogenicity of any intrauterine fluid. This examination and treatment of mares very soon after breeding before the bacteria have been long in a logarithmic growth phase is important for the susceptible mare. Treatment has been successful as early as 4 hours after breeding.

Intravenous administration of 25-30 i.u. oxytocin. After 20 minutes the mare should be re-examined and any fluid pooling in the vagina removed

Infusion of a low volume of water-soluble broad-spectrum antibiotics. The antibiotic combination I use is (neomycin (1g), polymixin B (40,000i.u.), furaltadone (600mg) and 3g crystalline benzylpenicillin (Utrin Wash, Univet Ltd., Wedgwood Road, Bicester, UK) dissolved in 30ml of sterile water) into the uterus via a sterile irrigation catheter. I use a relatively low volume of antibiotic solution as, if these mares have a drainage problem, it seems logical to use the minimum effective volume. It is my experience that with larger volumes (above 250 ml) much of the solution is lost via cervical reflux.

The mare is re-examined the following day and oxytocin treatment repeated if fluid is still present if the fluid has increased in volume, consideration should be given to performing uterine lavage

Obviously it is impossible to be certain of the importance of each component of this management protocol, but results have indicated the benefit of this management regime in mares in which sub fertility is associated with intraluminal fluid. A series of eleven mares were described initially (Pycock 1994) but I have since used the technique with much success over the following three years in brood mare practice. In some mares the incorporation of large-volume lavage will be beneficial.


These protocols are difficult to apply where breeding farms are not being visited every day and are best reserved for the highly susceptible mare. Susceptibility to endometritis is not an absolute state: failure of the defence mechanisms only needs to be of the degree necessary to slow the process of clearance past a critical point. As many stud farms are visited on an every other day basis for routine reproductive work, treatment schedules should be based round these visits. In my experience this approach can enable pregnancies to be initated and maintained with the birth of healthy foals from mares which would previously have been considered unable to breed any more. The approach can be applied by the veterinarian in practice and should help in his other equine breeding work.

Summary practical management of the susceptible mare

Use ultrasound evaluation of the uterus for detection of intraluminaluterine fluid, in addition to conventional techniques of endometrialcytology and bacteriology, before breeding. If more than one inch of fluid is detected, administer 3 ml oxytocin as an intravenous bolus. Confirm that the fluid has gone at the next ultrasound examination. If intraluminal fluid is still visible, repeat the dose of oxytocin and, possibly, digitally dilate the cervix also. Ensure good management techniques at all times. Particular regard should be paid to:

        Attention to Hygiene:

        ) at breeding

        ii) use a tail bandage;

        Wash the mare's vulva and perineal area with clean water, ideally from a spray nozzle which avoids the need for buckets;

        ii) at foaling: examine all mares post partum for the presence of trauma which might compromise the physical barriers to uterine contamination

        iii) at gynaecological examinations: examinations per vagina should be perform edasaseptically as possible.

        Correct timing of breeding: This should ensure the minimal number of breedings.

        Correction of any conformational defects.

        Evaluation of the uterus post-breeding: This is a crucial time to assess the uterus of all mares and too many clinicians fail to evaluate the uterus post-breeding 


Pycock, J.F. (1994) A new approach to treatment of endometritis. Equinevet.Educ.6, 36-38.

Pycock, J.F. and Newcombe, J.R. (1996) The relationship between intraluminal uterine fluid, endometritis and pregnancy rate in the mare.Equine Pract. 18, 19-22.

 This article was produced by Dr. Jonathan F Pycock, B.Vet.Med., Ph.D., D.E.S.M., M.R.C.V.S. of Equine Reproductive Services who provide a wide variety of services, including:

Routine Gynaecological Monitoring of Mares

Treatment of Problem Breeding Mares

Evaluation of Stallion Fertility

Barren Mare Clinics

Artificial Insemination (Chilled and Frozen Semen)

Management of Older Breeding Mares

Behavioural Problems in Mares


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