Breeding your mare – How to achieve the best outcome for you and for her

So you have a broodmare?

There are so many things to consider! A choice of stallions, artificial insemination or live cover, when to breed, and veterinary costs associated with breeding? The list goes on!

Ultimately, we want to increase the reproductive efficiency of our broodmares to achieve a healthy foal 340 days later. But how can we achieve this? As the mare is seasonally polyestrous, the opportunity for breeding is often limited to long daylight hours in the spring and summer. The reproductive cycle of the mare repeats itself during this time, every 21 days until she is pregnant or the daylight hours become shorter again. The mare then stops cycling and her reproductive system remains dormant throughout the shorter day months of autumn and winter. There is always an exception to the rule and some mares are known to cycle year round. This most commonly occurs in northern Australia or when mares are housed under lights. However, most mares will start to cycle in in early spring in Australia.

Getting your mare ready for the breeding season

It is important that your mare is in good body condition for breeding. Most importantly, she should not be overfat. Mares who carry excess weight may have trouble falling pregnant. Ideally, the mares should be in light condition, with a body score of 2.5/5. This allows us to have the mare on a rising plane of nutrition whilst she is getting ready to be bred.

When your mare starts cycling, it is recommended that they have a breeding soundness evaluation performed by your veterinarian. This would include an ultrasound examination of the reproductive tract, a speculum or manual examination of the vagina and cervix and swabs taken for uterine and clitoral culture. This allows abnormalities to be identified at the beginning of the breeding season and addressed before breeding of the mare is attempted. If you have not noticed that your mare is cycling before the end of September, it is important that the mare has an examination to ensure there are not any obvious reasons for the mare not coming into season such as an unexpected pregnancy! Furthermore, not all mares are obvious when displaying signs of being in season or “oestrous behavior”. Your veterinarian should be able to determine the stage of her cycle by an ultrasonographical examination of her uterus.

In addition, to ensuring that the reproductive tract is in good working order it’s prudent to arrange for all routine care be done before starting the breeding process. This would include yearly vaccinations, a dental checkup and deworming. What’s good for the mare is good for the foal!

When is the best time to breed your mare?

Breed early and breed often! A pregnant uterus is a happy uterus! If you can afford to give your performance mare a year off early in her career to carry a pregnancy, success rates for your mare later in her life will be much higher. The aged maiden mare (10 yrs +) has her own set of problems including fibrosis of the cervix, persistent endometritis (inflammation/infection of the uterus) and reduced uterine clearance. Many of these problems can be reduced or avoided by allowing the mare to carry a pregnancy to term earlier in her life. If you have an older maiden mare, it is important that you work closely with your veterinarian to improve your chances of achieving a positive outcome. This may include better timing of breeding in relation to ovulation and management of the mare post breeding to ensure that the uterine environment is in a perfect condition for support of the pregnancy.

Live cover

There are many advantages to live cover breeding depending on your situation. The important things to remember is that the mare needs to be in standing heat/oestrus and willing to take the stallion at the time of service to prevent injury to those handling the horses, as well as both stallion and mare! This can most easily be achieved by routine scanning in addition to teasing of the mare to ensure she will stand for service. Sperm can last in the female tract for up to 72 hours so the mare needs to ovulate within this time frame following service. Ideally the mare should ovulate within 48 hours following natural cover. The best way to ensure this is to have your mare scanned to determine ovulation in addition to the use of ovulating agents such as Deslorelin (Ovuplant™ or Bio Release™Deslorelin) or Chorulon™. In addition to identifying ovulation, your veterinarian can also use the ultrasound to examine the uterus to ensure there is no inflammation or fluid present following breeding. Some stallions are available for live cover more than once during the cycle and owners may elect to continue to breed throughout the mare’s cycle while she continues to stand for service. Routine scanning of these mares is often not performed as it is assumed that the mare has ovulated as she will no longer take the stallion. However, it is very important that the mare is scanned for pregnancy diagnosis 14-16 days after the last date of service for the early detection of twins. There is a very small window of opportunity between 14-17 days post ovulation where twins can be identified and reduced safely, ensuring the maintenance of a single pregnancy. The success rate of live cover breeding is dependent on the inherent fertility of both the mare and stallion. In intensively managed thoroughbred broodmares up to 65% per cycle conception rates have been reported in the northern hemisphere1,2 while per cycle pregnancy rates up to 70% have been achieved in Australia3

Chilled semen insemination

There are many advantages of using artificial insemination, in particular chilled semen insemination. This allows breeders to have their mare’s managed by their local veterinarian whilst taking advantage of superior genetics that may be located elsewhere in the country. Chilled semen insemination reduces the need to transport valuable livestock and minimizing risk to the mare during the actual breeding process. There are a few points to consider when breeding your mare with chilled semen. It is important for mares to be intensively managed by your veterinarian in order to maximize the chances of pregnancy. Ideally, mares ovulate within 12-24 hours post insemination with chilled semen remembering that the semen was most likely collected 24 hours prior to its arrival at your veterinary clinic and has a short life span following collection. Attempting to coordinate mare ovulation, stallion semen collection and courier companies to organize transportation of the semen can often be tricky. It is recommended that you are aware of the risks associated with semen transportation as it often causes frustration, particularly in remote areas. However, if managed appropriately, breeders should be able to reap the benefits of 65% per cycle pregnancy rates4, similar to that of live cover with significantly less risk.

Frozen semen insemination

Frozen semen has had a lot of bad press over the years due to a lack of quality control in the cryopreservation of semen, poor post thaw handling of semen and inexperienced AI technicians. The advances of ultrasonography and increased use of ovulation induction agents have significantly increased success rates with the insemination of frozen semen in addition to improved cryopreservation methods and quality control programs such as Select Breeders Services (SBS). Success with frozen semen insemination of course relies on a number of factors including both mare and stallion factors and also technician factors. In order to maximize pregnancy rates it is important that an experienced reproduction veterinarian be allowed to set the mare up and breed her at the ideal time. In general, mares bred with frozen semen have a slightly (~10%) lower first cycle pregnancy rates (51.3%) in comparison to chilled semen inseminations (59.4%). However in this same study, performed by the SBS laboratory in Maryland USA, end of season pregnancy rates were slightly better for frozen semen (75.6%) compared to chilled semen inseminations (74.7%)4. Historically mares have required an increased number of scans to allow accurate timing of insemination with frozen semen. Now, using timed insemination protocols and ovulation induction agents, mares can be managed in a similar manner to chilled semen inseminations. However, it is important to remember that not all broodmares are suitable for artificial insemination with frozen semen. In older and problem mares, pregnancy rates with frozen semen are lower than insemination with chilled semen. In these mares it is recommended that a stallion with known good fertility is used either via natural cover or chilled semen insemination.

1. Morris, LHA, Allen, WR (2002) Reproductive efficiency of intensively managed Thoroughbred mares in Newmarket, Equine Veterinary Journal, 34: 51-60
2. Bosh, KA (2006) Reproductive efficiency of thoroughbred mares in Central Kentucky, Journal of Equine Veterinary Science, 26:192-3
3. Nath, LC, Anderson, GA, McKinnon, AO (2010) Reproductive efficiency of thoroughbreds and standardbred in North-East Victoria, Australian Veterinary Journal, 88: 169-175
4. Squires, E.L, Barbacini, S., Matthews, P., Byers, W., Schwenzer, K. Steiner, J. and Loomis, P.R. (2003) Retrospective study of factors affecting fertility of fresh, chilled and frozen semen, Equine Veterinary Education, 18:2, 96-99