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Equine reproduction…all you need to know about putting your mare in foal

Emma Seamark BVetMed (Hons) MRCVS, St David’s Equine Practice

Breeding cycle of mares

The breeding cycle of mares differs to that of cattle and humans as they are seasonal breeders and so will only cycle during certain times of the year, but will have multiple cycles during this time. The non-cycling period is called anoestrus and is usually between the months of October and February. The natural breeding season for mares in the UK is between March and September and the increasing day length during spring time stimulates the mare to start cycling and coming back ‘into season’.

The normal mare will have multiple cycles during the breeding cycle, each cycle lasting approximately 21 days, with periods known as oestrus and dioestrus. The period of oestrus lasts for five-seven days and during this time the mare will show signs of being ‘in season’ such as frequent urination, clitoral eversion (‘winking’) and willingness to be served by the stallion. The remainder of the breeding cycle is known as dioestrus and the mare will be non-receptive to the stallion.

What do I need to consider before putting my mare in foal?

There are many factors to consider when breeding from your mare, including temperament, conformation, age and body condition. Temperament can be affected by environment and management, however certain traits are inherited so this is an important factor  to consider. Many conformational traits can be inherited (desirable and undesirable) so it must also be considered whether these may be passed on to the foal Age has considerable effects on a mare’s fertility. Success rates are higher in younger mares with peak fertility between five and twelve years old. It is also not advised to breed from immature fillies as this can impact on their growth and development.

Before breeding from your mare you will need to decide which stallion you wish to use depending on breeding, temperament and the form in which the semen is available. The availability of the semen will affect whether you can breed from your mare by natural cover or artificial insemination. Appropriate pre-breeding health tests All mares should be tested for Equine Viral Arteritis (EVA) and Contagious Equine Metritis (CEM) prior to breeding. EVA testing requires a blood sample and CEM testing requires a clitoral swab. Sometimes other tests are required such as a uterine swab, strangles ELISA blood test etc. It is also essential to ensure your mare is up to date with worming, flu and tetanus vaccinations as a minimum.

Pre-breeding reproductive examination and insemination
It is advised that your vet carries out a prebreeding reproductive examination to assess your mare’s suitability and whether there are any reproductive concerns that could affect her fertility. The most appropriate time for the pre-breeding examination is when your mare is cycling normally and has shown signs of being ‘in season’.

A pre-breeding reproductive examination will usually include examination of the udder, conformation of the vulva, examination of the vagina and cervix by speculum examination and ultrasound examination of the uterus and ovaries. The ultrasound examination is carried out internally by rectum. Any necessary health tests can also be carried out at this time. The pre-breeding reproductive examination will also assist your vet in determining at which stage your mare is in the breeding cycle. If your mare is in dioestrus, then a prostaglandin injection can be administered to shorten the time to bring her into oestrus. Once prostaglandin has been injected, your mare will then need to be frequently scanned to monitor the development of the follicles and ensure she is inseminated, or covered by the stallion cover, at the correct time.

Next time, we will cover different types of artificial insemination, pregnancy diagnosis and aspects to consider during the pregnancy and foaling.

St David’s Equine Practice provides the equine veterinary services for Molecare. Visit www.stdavids-equine.co.uk for more information.

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