The Role of the Stud Veterinarian

Hundreds of years of history testify to the fact that mares generally go in foal when covered by a stallion. So why is a stud veterinarian necessary?


The aim of the stud veterinarian is to achieve maximum mare fertility while protecting the stallion from over-use or injury.

In order to assist the veterinarian in achieving this aim for your mares it is necessary to understand the reproductive cycle of the mare.

Mares do not usually cycle all year round, with the average mare cycling from early spring to late summer / autumn when the reproductive organs shut down for the winter months.


The signs of heat vary according to the individual but it in most mares the behavioural changes are quite obvious.mare-oestrous-5

  • She may urinate in small amounts and usually hold her tail high for a longer time than normal after urination.
  • She may stand and rest with her tail slightly up or held to the side.

mare_winkingMares may also 'wink' or open and close the lower part of the vulva - especially when near a stallion. This is a sign that indicates to a stallion that the mare is ready to mate.

  • mare-oestrous-4
  •                 She may also spread her hind legs
  •                 and squat down, looking as though
  •                 she is trying to urinate

                                      - and she often does.



  • Mares often act differently toward other horses during oestrous.  She may pin back her ears, bite, kick, or chase away a gelding



Mares who are not in heat can be hostile towards a stallion and may kick, bite, or whirl away from him. This is why teasing (using a stallion to determine whether a mare is in season) must be done very carefully by experienced handlers so that the neither the stallion nor mare suffer injury. A mare in heat will act interested in the stallion, may nuzzle him, and will generally stand still for him to mount her.

Although in past years determination of heat may have relied upon a teaser horse and / or an experienced handler, today's reproduction veterinarian can determine the stage of the oestrous cycle of a mare with great accuracy by rectal examination using an ultrasound scanner. The uterus, cervix and ovaries will be examined and scanned to determine the presence of any fluid in the uterus. The size, shape and stage of the any follicles in the ovaries will help to predict the timing of ovulation and therefore when the mare should be put to the stallion. If artificial insemination  is to be used rather than natural service more scans will be necessary to recommend the optimal time for insemination using chilled or frozen semen.

Most mares start cycling (come into season or oestrous) in spring in response to the increasing length of the days. They then cycle every 21 days.  The oestrous period may be longer in early spring - commonly called a "spring heat" - with the length of the oestrous period decreasing as the season progresses. They remain in season from 3 to 7 days, during which time the mare will be receptive to a stallion. 

Cycling in wet mares mares (mares with foals at foot) begins with the foal heat which is usually around 9 days after foaling. (The foal may have diarrhoea during this time.)

Most mares ovulate or release an ovum (egg) from a follicle in the ovary on the last few days of the oestrous period. If the mare has been mated and semen is present, fertilization takes place in the oviduct (fallopian tube). The fertilized ovum remains in the oviduct for 6 days before entering the uterus. At the time of release of the ovum from the ovary, a corpus luteum is formed which secretes progesterone - a hormone which helps to maintain the pregnancy.

In summary:

A complete oestrous cycle is around 21 days long. It consists of:

1. Oestrus (receptivity to the stallion) lasting approximately 5 days
2. Ovulation (release of the egg from the ovary)
3. 24 more hours of receptivity following ovulation
4. Dioestrus (not receptive to the stallion) lasting approximately 15 days



Latest News & Events

Posted on 2014-12-15

• Farewell Angie & Dylan It is with great regret that I must announce that our friend & veterinary colleague, Angie Doudle (& her delightful son Dylan) will be leaving the practice at the end of the year to…  Read-on »