Tristan Starr, AI Technician, B.Sc.Agr (Hons)

The main aim of horse breeders every year is to achieve healthy, live foals from their broodmares. However, some broodmares have conception failures and pregnancy losses that result in the mare entering the next breeding season empty or barren. This proves very costly to the commercial horse breeders and heart breaking to the hobby breeder.

Presuming the stallion had normal fertility and the mares were managed effectively the cause could be put down to irregular mare sub fertility. Generally, this is caused by age related genital tract disease, obstetric injuries, poor reproductive conformation or abnormalities in the cycle activity of the mare.

In order to achieve maximum breeding efficiency in your mare, all 'problem' mares should receive a thorough examination prior to the next breeding season. Without this examination and thorough preparation, mares may continue to enter future breeding seasons with persistent genital or cyclical abnormalities that will result in treatment, recovery, delayed mating, all of which wastes valuable time and money.

In evaluating these mares all aspects of management should be taken into consideration. Nutrition, teasing techniques, parasite control, medical history, evaluation for chronic generalised disease and other management practices.

Reproductive History

It is essential for the mare's age and breeding history to be known to identify an accurate cause for poor reproductive performance. Is she a young barren mare that has had no history of conception or a 19-year-old mare that has had 6 foals previously with no adverse problems and suddenly suffered early fetal death or an abortion.

A mare is considered a 'problem' mare only when she fails to conceive to a fertile stallion on 3 or more cycles per season or continually loses her pregnancy.

Once the breeding history is known, a comprehensive examination can be performed to diagnose the causes for her reduced reproductive performance.

Bacterial Causes for Reproductive Failure

The ability to recognise factors responsible for mares' susceptibility to uterine infection and persistent uterine inflammation should considerably reduce the number of problem mares presented every year. Careful management to ensure prompt treatment or prevention of uterine inflammation is extremely important.

Mares do not become problem mares overnight, susceptibility to infection is a graded condition and occurs mostly due to effects of increasing age and bacterial challenge. Bacterial challenge is predisposed by external conformation, breeding techniques, examination procedures, anatomical abnormalities and post-foaling events.

The physical barriers that prevent infection are the external vaginal lips, vestibular sphincter and the cervix. The conformation of the mare's vagina, the shape and angle of slope in relation to the anus will all determine the chances of infection being introduced into the uterus. As a result of poor external and internal conformation uterine infection and uterine inflammation will occur. Some inflammation is a normal consequence of service, foaling and failure of physical barriers to prevent infection. However, inflammation that persists until the embryo enters the uterus (day 5-6) results in an unsuitable environment for embryonic development and ultimately loss of the embryo.

The aims of therapies to reduce bacterial contamination are to create a uterine environment capable of supporting a pregnancy and the prevention of further contamination. These therapies can be administered pre or post breeding and normally consist of uterine flushes containing antibiotics and oxytocin.


Figure 1a: Uterine Fluid
Figure 1b: Normal Uterus

Abnormal Cyclical Activity

The reproductive cycle of the mare is subject to the greatest variability of all the domestic animals. A variance in cycle activity can reduce the conception rates of a mare to zero. The main causes of abnormal cyclical activity are vernal transition, persistent CL (Corpus Luteum), silent heat, post-foaling anoestrus, haemorrhagic follicles, granulose cell tumors, chromosomal abnormalities or nymphomania.

  • Vernal transition is when a mare will show oestrus behavior and accept the stallion for days (even weeks at a time) without experiencing a normal ovulatory cycle. To diagnosis this condition regular reproductive examinations need to be performed. Treatment and management of these mares in vernal transition is often overcome with progesterone administration.
  • Persistent CL's can result in a prolonged off-season for the mare. A reproductive examination will reveal the CL on the ovary as well as a closed cervix and toned uterus. Treatment for this requires a simple injection of PG (prostaglandin).
  • Silent Heat and Post-Foaling Anoestrus generally occurs in maiden mares, first foaling mares or mares over protective of their foals. They do not show any behavioural signs of coming into season and they may not stand for the stallion. Management usually involves restraint of the mare or AI. Removing the foal is not an effective method of dealing with these mares as they generally get quite aggressive and stressed when they cannot see their foals.
  • Haemorrhagic follicles are caused by large follicles on the ovary that fail to ovulate. These follicles fill with blood and can take days or weeks to contract and form normal tissue again. Management of these haemorrhagic follicles involves identification of the structure in the ovary and monitoring its progress by ultrasound examination. Once a normal follicle is observed on the ovary, PG can be administered to return the mare to oestrus (usually within 3-5 days).
  • Ovarian tumors in mares are rare. The most common ovarian tumor in the horse is a granulosa cell tumor. These tumors are generally benign, however, they cause abnormalities of cyclical activity due to their active production of hormones. The hormones produced may result in mares showing persistent 'in season' behavior, no behavior or stallion-like behavior. The tumors can occur in mares of all ages but are most common in mares 5 to 9 years. Diagnosis requires rectal examination and ultrasound of the ovaries, the infected ovary usually being extremely large and firm therefore making it easy to palpate. Treatment of these tumors requires surgery to remove the effected ovary or ovaries and it may take years for these mares to resume normal cycling activity.
  • Various Chromosomal Abnormalities have been reported in the mare. These abnormalities result in irregular behavior or absent cyclical activity, they cause infertility, reduced fertility or structural abnormalities of the reproductive tract. Diagnosis can only be verified by karyotype assessment of a DNA tissue sample. It is highly recommended for a mare with a history of infertility and clinical abnormality to undergo a DNA assessment, as there is no cure for chromosomal abnormalities.
  • Finally, nymphomania is used to describe mares that demonstrate persistent oestrus behavior. Mares do not actually experience 'true nymphomania' as it exists in other species, it is just a word used to describe the behaviours a mare exhibits in her oestrus phase. There are 2 main clinical causes of persistent oestrous behavior, vernal transition and granulose cell tumors (these have been discussed earlier). In other rare cases, mares may have a psychological or behavioural condition that makes them display urine-squirting, tail raising or 'winking'. These mares can be treated with hormones to regain their normal behavioral characteristics.

Breeding Management

The best results are achieved when the mare is assessed and the problems identified prior to commencement of the breeding season. Abnormal cyclical activity can usually be managed and treated with administration of hormones or surgery prior to breeding. However, failure to treat an active chronic uterine infection during the non- breeding season is one more insult to an already compromised reproductive tract.

The primary goal at the beginning of any breeding season is to have a normal cycling mare and a uterine environment capable of supporting sperm long enough so they can reach the oviduct in a condition capable of fertilising the egg. This can only be accomplished with strict management practices pre and post breeding, correction of physical abnormalities, and treatment of infection and inflammation.

Few mares are truly infertile and with accurate diagnosis, rational treatment and careful management most mares can be encouraged to breed successfully.

Contact Us

Tristan Starr: 0400 816 072
Mathew Holz: 0417 409 029

105 Chambers Road, Modella Victoria 3816

About Us

Tristan and Mat run the Stallion & AI Center during the breeding season and break-in, train and compete their own and clients horses all year round. Read more...