Mares are seasonal breeders, and are therefore inactive in winter. As spring approaches, hormones in the mare’s body react to the increase in day-length, triggering oestrous.
This process is not always flawless. Initially, the mare may not cycle properly (she may come on heat, but fail to ovulate, a condition known as ‘transitional oestrus’), but this usually resolves itself within two weeks or so. If you mate your mare during transitional oestrus, she may accept the stallion, but not be ready to be in foal.
The mare’s oestrus cycle consists of five stages; your aim is to determine the one day (only one!) out of 21 when she ovulates. Begin by arranging for a vet to examine the mare. Then introduce a teaser stallion, and closely record her behaviour (see box).
Accuracy is key
At this stage of the year, you should have already started teasing. The goal is to inseminate the mare within a 12-hour period before and after ovulation.
In the wild, stallions cover a mare repeatedly when she in standing heat (a 3 and 4 on the 0-4 oestrus scoring scale), meaning that there are live sperm in the mare when she ovulates. With artificial insemination (AI), only a limited amount of semen is available, and you should therefore ensure that you inseminate the mare as close to the target date as possible.
The success rate of AI in horses is also influenced by the type of semen used (thawed, frozen or fresh), as well as its quality, quantity, fertility, morphology, activity and age, and the method of insemination.
When the mare has ovulated, and the ovum is unfertilised, she will go into dioestrus and show no interest in mating for most of her 21-day cycle (usually 15 days). She will then slowly come on heat again.
Most mares average five days on heat. This is where things get tricky; some don’t show heat at all! Ask a vet to perform a rectal examination of the mare, checking her ovaries and ripening follicles.
The right time
The mare will ovulate on the last of her days on heat. Don’t miss this! Insemination even a few hours after ovulation is invariably too late.
As the mare approaches scales 3 and 4, your vet should carry out another rectal examination, and preferably an ultrasound scan. If the follicles have ripened sufficiently, a hormone injection is an option to induce ovulation.
If the mare does not conceive, she will go into dioestrus again.
You must also inform the owner of the stallion providing the semen when ovulation is expected. Most vets perform two AI procedures a day; this increases the chances of success.
If the mare is cycling normally, other treatments, apart from a hormone injection to induce ovulation, may be unnecessary. Your vet can advise you in this regard.
Kim Dyson breeds Arabians and Lusitanos, and has 22 years’ experience in holistic equine and human body work.