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Reproductive Health

Understanding the basic physiology and anatomy of the brood mare will provide owners with information that is vital for successfully breeding healthy foals.


The mare has two ovaries that lie in the dorsal (upper) part of the abdomen, behind the kidneys. The ovaries are the female gonads and produce and release eggs. They are also the site of production of the female sex hormones oestrogen and progesterone. The uterus is comprised of two horns and a body, all being suspended from the roof of the abdomen by the broad ligament. The cervix guards the entrance into the uterus from the vagina.

The Oestrus Cycle

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Mares are 'long day' breeders and in the Northern hemisphere, generally, are most sexually receptive from April through to September. During winter the mares become sexually inactive and are in a state of anoestrus. As spring approaches and day length increases, a gland within the brain, the pineal gland, produces less of a substance called melatonin and the mare enters a transitional oestrus period. In response to rising hormone levels, follicles are stimulated to grow within the ovaries. Initially lots of follicles grow simultaneously until one becomes dominant and ovulates. After this, regular oestrus cycles will occur through the summer months. Each oestrus cycle lasts around 21 days with the mare being in season (sexually receptive) for 3-8 days. During this time the mare will show variable behavioural changes and will also be receptive to the stallion, allowing him to nuzzle her, whilst she shows signs of oestrus.

This picture shows a mare being teased by the stallion; this mare is in season and will be receptive to the stallion, note the tail off to one side and the urination that she is displaying as these are signs of oestrus.

These behavioural changes are due to increasing levels of the hormone oestrogen which is released from the follicles. Ovulation usually occurs 24-48 hours before the mare goes out of season and the follicle that has ovulated forms a structure called the corpus luteum within the ovary, which produces another hormone called progesterone. Progesterone, in simple terms, has opposite effects to oestrogen as the mare will now be out of season and aggressive towards the advances of the stallion. At around 16-17 days, the lining of the uterus produces a hormone called prostaglandin which destroys the corpus luteum and progesterone that it is producing. This reduction in progesterone allows follicles to develop again and the mare to return to season however if the mare is pregnant the corpus luteum will remain and along with other factors, allow pregnancy to continue and suppress further returns to cycling activity.

Preparing your mare for stud

There are a number of things that need to be considered before sending your mare away to stud. For more detailed information contact your local veterinary surgeon.

Breeding Soundness Examination of the mare

Prior to sending your mare to stud it is prudent to have her examined by your veterinary surgeon to ensure that she is fit to breed. To perform this safely your veterinary surgeon may require stocks although quiet, well-behaved mares can be assessed over a stable door.

The breeding soundness examination will include:

  • A physical examination
  • Rectal examination
  • Ultrasound scan
  • Reproductive examination

At the same time your veterinary surgeon will also be able to perform clitoral swabs and blood tests required by the stud to confirm that your mare is free of venereal disease.

Other General Considerations

Before sending the mare away you will need to consider whether the following are required and up to date:

  • Vaccinations (tetanus, influenza and herpesvirus (if required))
  • Worming control
  • Dental management
  • Shoeing
  • Overall physical condition of the mare

Also it is common practice for any new additions onto a stud farm to be isolated on arrival. This allows time for any incubating infections to be shown up. If your mare is pregnant and you are sending her away to stud to foal and be recovered, then you should contact the stud for further information as the mare may well need to arrive at the stud at least 3-4 weeks prior to her foaling date.

Your veterinary surgeon will be able to provide you with further information on both what is involved with a breeding soundness examination as well as providing advice on appropriate considerations for your mare.

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Mares can be mated or "covered" in one of two ways. The first and most obvious is when they are naturally mated. The second is where semen is collected from a stallion, which may even be on a different continent. It is then stored, and at a later date, placed into the uterus of the mare. This process is known as artificial insemination (AI).

Natural covering. Note the safety hat worn by one of the handlers.

Natural Mating

Mares are often covered naturally, especially in the thoroughbred industry. In some instances the stallion will be free to run with the mare whilst at other times the stallion covers the mare every other day whilst the mare is in season. Developments in the management of equine breeding mean that it is now possible for a veterinary surgeon to examine the mare to see what stage of her cycle she is in and then if deemed to be in season the stallion will be allowed to mate with her. The mare is then regularly rechecked for signs of ovulation and ultimately pregnancy.

Artificial Insemination (AI)

Within the non-thoroughbred industry, the use of AI is becoming more and more popular. Fresh, chilled or frozen semen can be used.

The advantages of AI include:

  • Reduced risk of spreading venereal diseases as there is no direct stallion-mare contact
  • Reduced risk of injury to the horses and handlers
  • Achieves mating whilst the sire and dam are on different stud farms, or even in different countries

Artificial insemination involves collecting semen from the stallion and then implanting it into the mare. The semen is collected by having the stallion mount a teaser animal or dummy. Once mounted, the semen is collected into an artificial vagina (AV) and then either used immediately or frozen, stored and then transported to the stud farm where the mare is stabled. The mare is then inseminated once she is in season. The semen is thawed (if frozen) and inserted into the mares vagina via a pipette.

If you are considering breeding from either a mare or stallion your veterinary surgeon will be able to provide you with further advice as to which method is appropriate for you.


Pregnancy describes the state of the mare following successful mating through to the act of giving birth, called parturition.

How long does pregnancy last?

The average length of pregnancy or gestation length is 340 days. In ponies it is slightly shorter at 333 days. However this can be a variable time period and a normal healthy foal may be born anywhere between 325-365 days gestation.

The length of pregnancy can be affected by various factors including nutrition; as well-fed mares will often have shorter pregnancies. Also, the time of year can have a bearing on how long a mare will remain pregnant as mares that are carrying foals through the winter months often have longer pregnancy or gestation lengths than those in summer.

How is pregnancy diagnosed?

The traditional method for diagnosis is rectal palpation where the foetus or foal is felt for manually. More recently ultrasound examination has become increasingly used as the foetus can be visualised on a screen and often the pregnancy can be detected earlier than with manual palpation. Ultrasound examination involves insertion of a probe that relays an image back to a screen which can be viewed and stored.

There are two types of blood test which can also be used to diagnose pregnancy. They both look for the presence of a hormone called equine chorionic gonadotrophin or eCG. This hormone is produced by the mare only during pregnancy between days 45 and 100 and there is also a urine test available.

Your veterinary surgeon will be able to discuss further the different methods of diagnosis and which one(s) are most appropriate for your mare.


Foaling is usually a relatively straightforward affair, however it is advisable that you consult your veterinary surgeon for more specific advice before your mare is due to foal. If possible, have an experienced friend available for when the time comes if you are not completely happy with the process.

In Preparation: Good Hygiene and a peaceful environment

For foaling, the mare will require a large well ventilated, draft-free box deeply bedded with clean, dust free straw. The clean manger should be supplied with fresh water at all times and good quality hay should be available to the mare ad lib. Her tail should be bandaged up just before foaling whilst her hindquarters, legs, vulva and udder should be washed with an antiseptic solution. Foaling will usually take place in the night when there is reduced activity in the yard and it is quiet and so some studs set up cameras so that the mare can be observed at all times without being disturbed.

The stages of foaling

Up to 24 hours before foaling the mare may start secreting a waxy substance on the udder and inside of the hindlegs, this is called 'waxing up' but is not done by all mares and often maiden (first foal) mares may not do this. The actual process of Foaling, or parturition, as it is called technically, can be divided into three stages:

Stage one:

During stage one, the uterus will start to perform contractions, moving the foal into the correct position. The mare may show restlessness, sweating and signs of mild colic including flank watching and getting up and down but there may not be many other external signs visible. It is important throughout this time not to disturb the mare.

Stage two:

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A normal assisted delivery. Note the white membranes encasing the foal.

The second stage of labour involves the breaking of the waters as the membranes around the foal rupture and release the fluid. More powerful contractions involving the abdominal muscles then begin and can be seen. After the waters have broken, the white membranes of the sac containing the foal will appear at the vulval lips. The foal should present for delivery with two front legs and with its muzzle resting on top of the fore legs (the diving position). The foal is then usually delivered within 20-30 minutes after this.

Stage three:

The third stage of labour is expulsion of the foetal membranes. This should occur within a few hours of foaling.

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After Delivery

In the womb, the foal does not use its lungs. At birth, the small air sacs in the lungs rapidly expand in its first breaths to clear the fluid from within the lungs and so the foal will gasp initially. The breathing rate is often initially rapid and then settles down after about 24 hours to approximately 30-36 breaths per minute. Following delivery the foal is usually able to perform the following:

  • Within 5 minutes the foal should be able to sit up and lift its head
  • Within 5-10 minutes the foal should have a strong suck reflex
  • By 1 hour the foal should be able to stand, initially with a wide based stance. It will then start searching for the udder.
  • Within 2 hours the foal should be able to suck well from the mare.

Any delays in the foal establishing a normal pattern of behaviour may indicate early signs of problems and so it is important that you contact your veterinary surgeon at any stage of foaling that you suspect problems.

During the foaling process the mare should, although she may not know it, adhere to the time indications given above. Any delay may indicate the need for emergency veterinary attention and you should never intervene if you are unsure or have not first consulted your veterinary surgeon for advice.

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The Newborn Foal

The initial first few hours are when the mare and foal need to form a strong bond. A mare will have a very strong instinct to look after her foal, therefore the foal-dam bond should not be interfered with if at all possible.

Any delays in the foal establishing a normal pattern of behaviour should be a concern and may indicate the early signs of problems.

What you can do to check that your newborn foal is healthy?

It is best to observe the foals’ behaviour and overall appearance closely. After your initial observations up close you will need to watch the foal undisturbed, preferably from outside the box. Once the foal has stood it should be nursing 5-7 times each hour. In between these times it should be exploring its surroundings, bonding with the mare and sleeping. Most foals should startle when you enter the box and run to hide behind its mother.

  • Is the foal bright and inquisitive?
  • Are there any signs of prematurity? For example a short silky coat, floppy ears, domed forehead, slack tendons and a small size.
  • Foals gums should be pink and moist.
  • Is the foal shivering from the cold? Weak or premature foals are particularly susceptible to feeling the cold as they have poor body insulation and energy reserves. They are not always able to regulate their body temperature.
  • Check that the foal is sucking correctly. Milk on the foal's head may means the foal is not nursing correctly, or the mare is producing more milk than the foal can ingest. Milk seen coming down the nostrils may mean problems like a cleft palate.
  • Have a close look at its legs. Are they straight and able to support the foal when it stands? Are they lax, windswept or contracted? If so, is the foal having difficulty staying up to nurse?
  • Does its chest expand normally, with both sides symmetrical with each breath?
  • Has it passed its first faeces – the meconium? This is the dark hard balls of faeces that are an accumulation (while in the womb) of allantoic fluid, gut secretions and cellular debris. Failure to pass this can result in complications such as colic due to impaction. After passing the meconium, pale coloured pasty milk faeces should now be passed. Colts that are overdue seem to be most at risk of meconium related colic.

Any deviations from a normal physical appearance need to be seen by a veterinary surgeon promptly.

The foal's immune system

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Your foal has been born with a naïve immune system that does not have antibodies to fight off infections. The mare's first milk or colostrum is vital for the foal's health over the next 3 months because it contains the vital antibodies that will be absorbed across the foal's gut to protect it.

Specialised cells in the newborn foal's gut are uniquely designed to absorb colostral antibodies for a short period of time. After 8-12 hours these cells close down and stop absorbing antibodies. Therefore it is essential that the foal sucks from the mare and receives the colostrum as early as possible within this time.

Observe the mare's udder prior to foaling; If starts secreting milk before the foal is born, it may be that she is losing her colostrum. In this case it would be advisable to collect and freeze it until the foal is born. The quality of this thick creamy coloured milk depends on its richness. Very rich, good quality colostrum contains higher levels of proteins. These proteins can be measured on a hand held instrument called a refractometer that your veterinary surgeon will have.

Maiden mares may have poor quality colostrum or inadequate amounts and so it may be advisable to make prior arrangements to buy some from a neighbouring stud farm if needed.

Foals that fail to suckle may need to have a stomach tube passed by the veterinary surgeon and given the stored colostrum. This should be done within the first 4 hours following birth.

Other preventative measures to ward off disease

Your foal will ideally need to have its first vet examination within 24 hours of being born. This examination will be thorough and include all the body systems to recognise the early signs of disease or abnormalities. These problematic signs may be vague and non-specific but can rapidly worsen if they go unnoticed. You should always remember that a foal is not just a 50kg horse – not only do they change and grow rapidly but they can get sick just as quickly.

Your vet will take into account the mare's breeding history, as abnormalities during the pregnancy can be dangerous to the foal. They will examine the mare's placenta carefully making sure that it has passed intact. Retaining either all or part of the placenta can quickly lead to infection in the womb and this can rapidly trigger toxic shock, which can be life threatening or result in complications such as laminitis.

They will also check the foal's navel, the umbilicus, for any swelling, continued wetness, a hernia, infection and to see if it has closed up properly. It will need to be dipped in an antiseptic solution. This helps to dry the navel stump and prevent bacteria from tracking up into the body.

A blood sample can be taken when the foal is at least 18 hours old, to determine if the passive transfer of antibodies has successfully occurred from the dam to the foal. This is called an IgG test. Other tests can determine if an infection or anaemia is present, as well as detect for other abnormalities.

In conclusion:

Good preparation before the birth will help minimise stress for you and your foal. Raising your foal will then be a rewarding and educational experience for you.

Foaling difficulties


Dystocia or difficulty in foaling is uncommon in the horse. However if problems do occur it is important that your veterinary surgeon is contacted as soon as they are noticed. Sometimes the foal can be manipulated within the mare to enable normal delivery but it may be that the foal has an abnormality that will make a normal birth impossible, such as contracted tendons. Your veterinary surgeon will make an initial attempt to correct any incorrect position of the foal but a horse is unlike a cow in that she will not be able to tolerate a large degree of manipulation without some damage to her reproductive tract. So, when manipulation fails, a caesarean section may need to be performed.

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Caesarian Section

Caesarean section in the mare is a major operation performed under general anaesthesia. The decision to perform a caesarean is one which only your veterinary surgeon can make with you.

Retained Placenta in the mare

The foetal membranes should be expelled within a few hours of foaling during the third stage of labour. Occasionally these may not be expelled, but retained and if the mare has not passed the membranes within a few hours of foaling, then veterinary attention should be sought. Retention of the foetal membranes can lead to complications including endometritis (infection of the uterus) and toxic laminitis.

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Pet health categories Reproductive system
Published: 09:43, 12 April 2013 | Updated: 05:27, 29 July 2013