Choosing a Stallion for your Mare: Equine Reproduction

Equine reproduction has become big business.  Although there are still many private owners with a single stallion living at home premises, increasingly commercial enterprises have been developed to cater for the growing market in horse breeding.  Mare owners can now choose from a bewildering array of potential sires.  Obviously, a multitude of factors should be considered when selecting a suitable stallion, including breed, size, temperament and conformation, but this article will concentrate on factors related directly to the breeding process.

Points to consider include:

  • Location of stallion and type of semen/service offered

  • Age, temperament, and previous breeding history of mare

  • Cost of purchasing semen/service

  • Cost of mare management

Pregnancies may be achieved by natural service, or artificial insemination (AI) using fresh, chilled or frozen semen.  Most breed societies allow the registration of foals conceived by either method, with the notable exception of the racing Thoroughbred.  Each method has advantages and disadvantages, and the decision should be made after careful consideration of the individual circumstances of your mare and yourself.  Veterinary input should be sought at the outset.


Natural service has a proven track record of resulting in pregnancies since the days of Eohippus!  If you are lucky enough to have a suitable stallion in your locality (or further away if you are prepared to transport the mare) this may be a good option.  Usually, less veterinary input is required, so costs can be lessened.  Your mare will need to be relatively co-operative to minimise the risks to the stallion and handlers.  For some small pony mares, natural service is the only viable option, due to the danger of performing per rectum examinations in very small mares, which are necessary in the AI process.

It is essential that your vet takes a clitoral swab from your mare (a simple, non-invasive procedure) before she travels to stud, to ensure that Contagious Equine Metritis (CEM) and other bacterial diseases are not passed on to the stallion during covering.  It is equally important to check that the stallion has been certified CEM-free at the start of the breeding season.   Also check with the stud if blood samples from your mare for Equine Viral Arteritis (EVA) or Equine Infectious Anaemia (EIA) are required.  (These tests will also be needed by some studs or clinics before a mare is admitted to the premises for AI – check early.) Mares which are to undergo natural covering should be carefully managed by the stud owner to keep the number of matings to a minimum and good hygiene should be a priority.  The overall risk of introducing infection into the uterus is higher with natural service than with AI.


Many stallions are not available for natural service but offer semen for sale, either as fresh, chilled or frozen semen. The risk to the stallion of a kick from a mare is eliminated and the risk of disease transmission from mare to stallion, and vice-versa, is reduced.  More than one mare can be inseminated from a single collection, reducing costs.  It may also be beneficial, from a training point of view, that a stallion in competition does not regularly cover mares. 

  1. Fresh semen may be used if the mare is resident at the same premises as the stallion.  Semen is collected when the mare is at the correct stage of her oestrus cycle and immediately inseminated via a pipette into the mare’s uterus.

  2. Chilled semen is ordered by the vet on the day before ovulation is expected to occur.  The stud collects the semen and processes it using filters, antibiotics and extenders, before chilling it to approximately 5 degrees Celsius.  It is sent via courier or postal service to the premises where insemination will take place the following morning.  This is usually practicable within the UK and sometimes when obtaining semen from mainland Europe.      

  3. Frozen semen can be delivered worldwide, and in recent years has considerably increased the choice of sires.  A large number of insemination doses can be obtained from a single collection and stored for years in liquid nitrogen, making it a very convenient method of semen distribution.  Stallions in regular competition need not have their schedules interrupted, and pregnancies can even be achieved using semen from a stallion which is no longer alive.  Unfortunately, not all stallions produce semen which survives the freezing process, although processing methods are constantly improving.  Pregnancy rates achieved using frozen semen are slightly lower than when using other methods, but are increased by new insemination methods, such as deep intrauterine insemination.  The use of frozen semen is generally recommended in relatively young, fertile mares.

A veterinary surgeon or BEVA qualified AI technician may perform the insemination of semen, but only a vet may legally carry out rectal examinations for ultrasound scanning.  Veterinary input is usually needed when chilled semen is used, and essential when frozen semen is chosen, in order than ovulation is closely monitored so that insemination may be performed at the time most likely to result in successful conception.

A final cautionary note – always check on what basis you are purchasing the semen, and what the financial implications will be should your mare not become pregnant.  Don’t assume that one service or insemination will guarantee results – the best pregnancy rates quoted by well-run studs and clinics are approximately 60% per cycle, so more than one attempt is often necessary even in normal mares.


The material contained in this website is presented for information purposes only . The material is in no way intended to replace professional veterinary care or attention from a professional veterinary surgeon. 

The advice given in any of our web pages cannot be used as the basis for a diagnosis or choice of treatment.

Clyde Vet Group advises that you should always consult a veterinary surgeon about any queries with animals under your care.

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