Preparing your mare for breeding

There are many factors to consider before you breed from your mare. It is important to consider the costs, time and expertise required to breed a mare and look after a foal.

  • Decide whether you are happy for your mare to go away to stud or whether you would prefer to keep her at home for service.
  • Think about what stallion you would like to use and what type of semen is available.
  • Find out if there are any periods over the breeding season when the stallion is not available.
  • Think about whether you would like the mare mated naturally or whether artificial insemination is more appropriate.
  • Think about where you would like the mare to foal down, are you prepared to do foaling checks through the night yourself? Or would you prefer her to foal down at a dedicated stud?
  • Ensure that you have the funds available to cover the stud fees and that you are financially prepared for complications.

It is important to ascertain whether your mare is a good candidate for breeding, with a normal and healthy reproductive tract. Knowledge of where the mare is in her oestrous cycle, and following her while in season will increase her reproductive efficiency. Fertility declines with age, so horses over 13 years of age who have not had a foal previously, or mares that have had many foals in the past, may find it difficult to conceive. It is also important to check for sexually transmitted infections even if your mare has not been mated in the past.
Whether you are having your mare mated naturally or via artificial insemination it is important to time the breeding accurately, close to ovulation, in order to increase the chances of conception and decrease the costs involved.

Clinical exam

It is important to check that the mare is in good physical health. A lot of brood mares have orthopaedic (a musculoskeletal) disease that prevent them being ridden. It is essential to ensure that the orthopaedic problem is not likely to get significantly worse as the mare gets heavier in foal. A severely lame and painful pregnant mare is a welfare issue and the stress of orthopaedic pain may result in abortion. Any systemic medical issues such as cushings disease, insulin resistance should be addressed. Brood mares should be the correct weight with a body condition score of 5-7 out of 10; a mare that is either too fat or too thin will struggle to conceive.

Vulvar exam

One of the most important parts of the reproductive tract that is frequently overlooked is vulvar conformation. The vulva, along with the vestibulo-vaginal sphincter (hymen) and the cervix form the three barriers of the uterus that prevent contamination from air and faeces. The vulva should be vertical with the anus above it. In some older mares the anus becomes sunken and the vulva forms a shelf underneath – this is poor vulvar confirmation and makes uterine infection and inflammation more likely, reducing the chances of the mare to conceive.

Vaginal exam

It is necessary to examine the cervix and vaginal walls; this is done by placing a speculum into the vagina. Observing the cervix visually allows determination of where the mare is in her oestrous cycle, as well as if signs of inflammation (redness), infection (discharge) or if pooling urine is present. It is important to check the cervix for scarring which can result in difficulty dilating which can lead to fluid being trapped within the uterus as well as potential complications at foaling. The ability of the cervix to close completely without any defects is also necessary. If the cervix doesn’t close properly it allows contamination of the uterus potentially leading to chronic infection and inflammation. When checking for cervix competency, it is important to do so manually when the mare is not in season, so that the tubular canal can be felt completely.

Rectal exam and scanning

Mares are long day breeders and therefore their natural breeding season is in the spring and summer. Artificial lighting with or without medical treatment can help advance their return to reproductive activity. Rectal palpation and ultrasound allows the ovaries, uterus and cervix to be evaluated anatomically and functionally. Ultrasound gives the ability to see things within the reproductive tract which cant always be felt. Ovarian structures (follicles, corpus luteum, etc.), uterine oedema, intra-uterine fluid, and endometrial cysts are all important to note during the examination. Putting the whole reproductive exam together can provide you with the knowledge of whether your mare has a normal reproductive tract and cycle which aids in preparing her for breeding, as well as providing her with the best chance for conception.

Blood tests

Every mare should be tested for Equine Viral Arteritis (EVA) prior to breeding and only bred with disease free stallions. EVA is a sexually transmitted infection that causes abortion, and can cause flu-like symptoms.

Clitoral swabs

These are used to test for Contagious Equine Metritis (CEM) which is a sexually transmitted bacterial infection. It prevents mares conceiving, but may not produce any other outward signs and can therefore go undetected. All mares should be swabbed prior to breeding and only bred with disease free stallions.

Uterine culture and cytology

Uterine culture and cytology are important in identifying infection and inflammation. A culture provides evidence that bacteria, fungal or yeast infections are present. Cytology helps determine if inflammatory cells are present, in addition to bacteria, fungus, yeast, debris and mucous. A mare can have endometritis (inflammation of the uterus) with or without infection. It is important to identify inflammation since causes of inflammation alone can decrease a mares ability to conceive. Whether a culture or cytology is required prior to breeding, is determined by the stud/farm requirements, stallion contracts, and most importantly by the mare – if she has a poor reproductive history, any evidence of abnormalities on reproductive examination, or problems foaling, then these procedures are highly recommended.

Uterine biopsy

Uterine biopsies aid in determining the underlying health of the uterus. It provides information with respect to what problems need to be addressed and the probability of the mare carrying the pregnancy to term. Endometrial biopsies are recommended for mares that have a poor reproductive history or a history of foetal loss or abortion.

Once your mare has undergone her pre-breeding reproductive exam, and any recognised problems have been addressed, she can be prepared for breeding.
The chances of her conceiving are higher if mating is timed to coincide with ovulation. It is a good idea to keep a diary of when your mare is in season, as this will help the vet determine whether she is cycling normally. Palpating and ultrasounding her ovaries, uterus and cervix will enable the vet to track follicle development and uterine oedema with cervical softening, to help predict when she will ovulate. Once ovulation is imminent the mare can either be taken to the stallion or the semen can be ordered. It is important to know how long in advance stallion managers need notification for semen to be shipped. In addition, making sure frozen semen is accessible when needed is imperative. It may be necessary to examine the mare twice or even three times daily in the run up to ovulation if frozen semen is used.

It is possible to detect a pregnancy using ultrasonography as early as 11 days after ovulation. Most vets recommend ultrasound examination at 14 or 15 days post-ovulation, during the stage when embryos are still able to move. This allows identification and resolution of twin pregnancies if they are present.
It is recommended to have your mare scanned again between day 28-30 and day 42-45 to check for a heartbeat and to assess foetal viability. Unfortunately,  if the mare loses the pregnancy after day 40 it is highly unlikely that she will cycle again normally and therefore will not be able to be bred again that season.
Foetal sex determination can be performed between 58-70 and 110-120 days if desired.
Gestational length is incredibly variable in the mare ranging, on average, from 320-340 days.