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The mare is seasonally polyoestrus i.e. she has many breeding cycles at a distinct time of the year, usually from April to October. Most non-pregnant mares pass into anoestrus (a non-cycling stage) during winter at which time they cannot become pregnant.

Factors that stimulate the mare to cycle are:

  • Increased daylight.
  • Increased environmental temperature.
  • Increased food supply.
  • Pheromones (odours) from the stallion.

Many of these factors can be manipulated to encourage the mare to become reproductively active at non-favourable times of the year.

A variety of hormones are responsible for controlling the mare’s reproductive cycle and pregnancy, they too can be manipulated to control the mare’s reproductive cycle. This is particularly important when carrying out artificial insemination and embryo transfer.

The Horse Race Betting Levy Board (HBLB) recommends that all mares should be swabbed for Contagious Equine Metritis (CEM) and blood tested for Equine Viral Arteritis (EVA) after the 1st January of each year before they are taken to stud. These venereal diseases are highly contagious and are notifiable by law. Some studs have different requirements concerning the timing of swabs and blood tests and should always be consulted first; many studs now insist on a Coggins Test (for Equine Infectious Anaemia following the recent Irish outbreak).

A single clitoral swab can be taken at anytime during the mare’s cycle. In pregnant mares the swab may taken before or after foaling. (A second, endometrial swab, ie from the uterus, will be taken when the mare is in season just before covering.)

A single blood sample should be taken at a minimum of 28 days before the mare is being used for breeding activities. Breeding can only commence if no antibodies are detected. If the blood sample is positive a second blood sample is required.



  • Ultrasound scan



The most effective method of early pregnancy diagnosis is by ultrasound scanning per rectum. The first scan should take place between 15-17 days. At this stage, only a small foetal sac can be seen but it is important to detect the presence of twins as early as possible. A second scan should take place between 28-30 days as, at this stage, missed twins can be more easily identified and a foetal heartbeat can be detected. It is important to carry out a scan at this stage because if the foetus has been absorbed (aborted) then a further attempt at getting the mare in foal can be made in the same breeding season. Further scans can be carried out at later stages of pregnancy for determining foetal sex or to satisfy insurance needs.


  • Blood samples



      • Measuring plasma progesterone at 18-25 days but can get some false positive results.
      • Measuring serum ECG at 50-100 days but can get some false positives.
      • Measuring plasma oestrone sulphate after 100 days is more reliable.


  • Urine samples



Measuring oestrone sulphate after 100 days.

The gestation period of the horses is approximately 11 months but can range from 315-340 days in ponies and 320-360 days in the horse. It is not unusual for the gestation period to extend well over 365 days.

The pregnant mare should be wormed as part of a routine programme. She will have a reduced immunity to worms toward the end of the pregnancy. There are a variety of wormers available on the market at present and not all are safe to use in the pregnant or lactating mare. Once the foal is born, both mare and foal should be turned out onto clean pasture to reduce the risk of infecting the foal. Foals do not require worming until they are 4-6 months old, please contact Priors Farm for further advice on which wormers are safe to use in pregnant mares, lactating mares and young foals. Read more about Worming >

Influenza and tetanus vaccines should be kept up to date as in non-pregnant animals. It is advisable to have the mare vaccinated in the last 4 weeks of pregnancy to ensure that the antibodies for the diseases are at high levels in the colostrums when the foal is born. Read more about Vaccinations >

The Equine Herpes Virus 1 and 4 (EHV1, 4) viruses cause respiratory disease and abortion. The vaccine is not essential but is advised to be carried out in high-risk mares particularly those kept in large groups of breeding stock or those stabled close to young horses in training. EHV abortions usually take place after 5 months of pregnancy until birth, thus the requirement of EHV1, 4 vaccinations is at 5th, 7th and 9th months of pregnancy.

Teeth and Feet
Teeth and foot condition should be maintained as in non-pregnant animals. Dental examination should be carried out annually to determine whether rasping is required. Many brood mares are not shod and should have their feet trimmed every 6-8 weeks depending on horn growth.

The spring grass will meet much of the pregnant mare’s nutrition and so supplementary feeding is dependant on the quality of the grazing. In the first 7 months of pregnancy the nutritional requirements of the mare remain similar to when she is non-pregnant but vitamin and mineral supplements are essential. Overfeeding during early pregnancy is a common problem causing obesity; it may contribute to problems during birth and problems associated with getting the mare back into foal the following year.

In the last 4 months of pregnancy energy requirements increase by 15%, there is also a further demand for protein, vitamins and minerals. Rapid growth of the developing foal reduces the mare’s appetite. At this stage it is advisable to feed an increasing level of stud mix cubes. Please follow the manufacturers guidelines or contact Priors Farm for further guidance.

Once foal is born lactation is the most energy demanding time for the mare. For the first 3 months the mare produces approx 15 litres of milk per day this decrease once the foal is 3 months old. A high level of nutrition should be maintained for the first 3 months of lactation then gradually reduced. Weaning usually takes place when the foal is 6-8 months old. Read more about nutrition from Dodson and Horrell >

Towards the end of gestation there are important changes that take place that can be helpful in determining when the mare is likely to give birth. Information about the mare’s previous pregnancies can be useful as certain behaviours can be characteristic to a particular mare.

  1. Increase in abdominal size
  2. Perineal changes. Vulva relaxes several days before birth. Muscles and ligaments soften either side of tail head several days before birth. It is advisable to feel either side of the tail head daily 3-4 weeks before birth to detect changes in the muscle tone.
  3. Mammary gland changes. The udder starts to develop approx 2 months before birth but there is a vast increase in size 2 weeks before. The teats become short and fat but then elongate closer to birth and are more sensitive to touch. Oedema (fluid filling) is normal around the udder as they develop. A bead of colostrum at the teat tip (waxing up) indicates that birth should occur in the next 24 hours. Sometimes mares may run milk before birth and waxing up cannot be seen. In such cases the colostrum should be collected and stored to ensure a plentiful supply once the foal is born.
  4. Vaginal discharge. Fairly common in late pregnancy but check the mare’s temperature and seek veterinary attention as the discharge may indicate there is a problem with the unborn foal.
  5. Behavioural changes. The mare becomes restless and will move away from the rest of the herd just before birth.

Other monitoring systems are available to make it easy to tell when the mare is about to foal. These include sweating alarms and milk predictor test kits; please contact the practice for further information.

It is important that you too are prepared for the mare’s impending birth. She should be taken to the premises or stable where she is to foal at least 1 month before the due date. When any of the changes described above (1-5) are noted, the mare should be moved to a foaling box or large stable (approx 3x3m, bedded on straw, not shavings!) where she can be monitored day and night. Native pony mares foaling in the summer are best foaled out in the paddock.

Foaling Box

  • Ensure it is clean and disinfected.
  • Clean and very thick straw bedding, as little dust as possible.
  • Warm but with good ventilation.
  • No sharp edges that are likely to cause injury.

Foaling equipment

  • Naval dip – Hibiscrub.
  • Stored colostrum if mare has been running milk.
  • Towels.
  • Milk bottles and horse teats.
  • Thermometer.
  • Hot and cold water.

Signs of First Stage Labour; determining when the mare is foaling.

  • May last minutes to hours, a lengthened first stage may indicate problems.
  • Sweating – can be profuse or patchy.
  • Pawing the ground or flank watching (signs similar to colic).
  • Pacing around the stable.
  • Clamping tail.
  • Curling top lip (the Flehmen response).

Second Stage Labour

  • Should last 20-30 minutes, a lengthened second stage may indicate problems.
  • Waters break’ brown/yellow fluid passes through vulva.
  • Ends when foal is born.


Third Stage Labour

  • Passage of placenta (after birth) should occur within 6 hours. The placenta should be kept in a bucket for your vet to examine at the foal check the following day.
  • If the placenta has not been passed within 3 hours then tie those membranes that can be seen to prevent them being stood on and torn and call the office to speak to one of the vets.

Once the foal has been born and they both appear to be healthy leave them alone for about 15 minutes. When entering the box do so quietly and reassure the mare with your voice. Once she is happy that you are present check both mare and foal to make sure there are no obvious abnormalities. The foal’s navel should be immediately treated with dilute hibiscub. The mare and foal should be left alone but observed regularly. This allows a strong bond to develop between the mare and foal.

A healthy foal should attempt to stand within the first 30 minutes of birth. The foal should have learnt how to suckle and be feeding at regular intervals between one and a half and 4 hours after birth. It is important the foal feeds during this time to obtain the vital antibodies present in its mother’s colostrum. These antibodies are essential in defending the foal from disease in its first few months.

Meconium should be passed within 4 hours of birth. This will be dark brown in colour and hard and the foal will strain to pass it. Once passed successfully, the droppings become yellow in colour and softer in texture.

If the foal is not standing within 30 minutes, is not sucking within 4 hours, if the meconium is not passed within 4 hours or if the foal appears to be straining excessively please call the office and speak to one of the vets.

Once the foal is born you should contact Priors Farm to arrange a post-foaling examination for the mare and foal.

Post-foaling examination
We will examine both the mare and the foal thoroughly. The foal is checked to see if there are any serious abnormalities such as entropion (inverted eyelids) and the mare checked to identify if her birth canal has been damaged during foaling. We will usually wait to confirm normal foal sucking behaviour after the physical examination.

The placenta is examined to make sure that it is complete and that there are no abnormalities. If you observe the mare passing the placenta, please gather it up and keep it out of the box so that it can be examined as intact as possible.

The foal is given tetanus anti-toxin and an antibiotic injection. We will repeat the navel treatment. The navel should be treated twice daily for 3 days to help prevent any infection entering through the umbilical stump.

It is a very good idea to handle the foal as much as possible during the first 48 hours and then from day 2 to put on a foal slip. This will make life a great deal easier later on!

A newly born foal drinks 7-10 times per hour when it is first born to ensure it has enough energy to support thermoregulation and growth. The most rapid growth occurs in the first month. In the first 3 months of life, the foal requires a milk only based diet to reduce the chance of diarrhoea. If the mare’s milk needs supplementing at this time, then a correct milk based product should be used; a young foal may show interest in eating other foods when the mare’s milk quality is inadequate. Foals will graze from a few days of age.

From 3 to six months of age, high fibre feeds such hay can be introduced; the ration should be given according to the foal’s condition score and size. From 6 months and older, the foal’s intestines undergo their greatest development, meaning they do not require milk products and can digest foods similar to that of an adult. As foals are much smaller, they cannot consume as much as an adult and need highly concentrated diets and mineral supplements. We advise the use of a manufacturers’ product for the foal, weanling and yearling and follow their feeding guidelines or contact Priors Farm for further advice.

It is very common for foals to develop diarrhoea, “scour”, when 1 to 2 weeks old and this frequently coincides with the mare’s “foal-heat”. This diarrhoea is usually of no concern so long as the foal continues to suck strongly and remains bright and alert. It is now thought that the foal develops diarrhoea because at this stage the foal has started to eat its mother’s droppings in order to populate its intestine with essential bacteria required for digestion. No action is necessary apart from washing the foal’s hind quarters to prevent scalding from the diarrhoea. If you are concerned, please talk to one of the vets.

Vaccinations Influenza and tetanus vaccination can begin at 4 months old but maternal antibodies obtained from the mare’s milk may interfere with the vaccination, therefore it is better to start the programme once they are 5 months old. Please see the vaccinations section. Read more about Vaccinations >

Worming Worming can begin at 4-6 months old, before this time there is little risk of infection as the foal will not be grazing and will obtain much of its nutrition from the mare’s milk and the mare should have recently been wormed before foaling to reduce the risk of infection. Please contact Priors Farm for further advice as not all wormers are safe in foals that are as young as 4 months old. The foal should then be included as part of a complete worming programme; please refer to our notes regarding worming. Read more about Worming >

Castration – ‘gelding’ Colts can be gelded from any age but the risk of complications increases with the very young colt or the older stallion. There are two castration techniques; the standing technique with local anaesthesia or surgery under general anaesthesia. The method of castration used depends largely on the risk of complications post surgery and the size of the colt being ‘cut’. The surgery can be carried out either in the field or in the hospital. Please call the office and ask to speak to one of the vets if you have a colt to geld.

DISCLAIMER: This advice is intended for use by registered clients of Priors Farm only. The advice offered is general advice only. Priors Farm clients who wish to discuss the individual circumstances of their horse should contact the office. To speak to a vet please phone between 8.30 – 10.00 am on weekday mornings.