Ask the Vet: Reproduction

Answered by. Madison Seamans, DVM, MS, Kuna, Idaho, Courtesy of AAEP

Question: I have a mare with a four-day heat cycle. Are there any symptoms that might present before the normal signs of heat in order to give me a heads up? It isn’t possible to organize with breeders to obtain cooled semen from out of state breeders.

Answer: The use of shipped semen has greatly expanded the gene pool available to mare owners. It is now possible to have a mare bred to a stallion living half way around the world by shipping the semen, rather than the mare. However, this requires careful management to insure the best chance for conception. The most important aspect of mare management is heat detection.

A four-day cycle in a mare can be explained in a couple of ways: either a seasonal transition or uterine infection. Mares are seasonally polyestrous. This is an eight-dollar term meaning they cycle during the long days (spring and summer) more than once. A mare normally shows heat for seven days and is “out” for fourteen days. Therefore, the time between ovulations is about twenty one days.

Late winter and early spring is an interesting, and frustrating, season for mare owners. This is called “transition”: that period between the non-cycling and cycling seasons. This is characterized by erratic, irregular heat periods, like the four-day period in question. Although transitional mares will often stand to be mounted, these periods are not true “cycles” and are not fertile. Even though some mares will display dramatic heat signs in February and March, the average date of first ovulation is April 1, under natural lighting conditions.

Some mares will show heat to a gelding or even other mares. However, the most reliable method of tracking their cycle is with daily teasing and record keeping. A “teaser” stallion can talk to the mare and she will respond when she is ready to be bred. Good broodmare monitoring requires diligent, accurate observation on a daily basis. This will greatly enhance our ability to determine:

1. When she is ready to breed
2. Whether or not she may be in foal
3. When she may be coming back into heat
4. Or developing a uterine infection.

If no stallion is available, a trained equine veterinarian can examine the mare to determine where she is in the three week cycle. (This requires a long plastic glove and a little nerve) There are several different hormonal treatments available that will allow us to induce heat and ovulation. This will help us to more accurately synchronize ovulation with the delivery of shipped semen. Fertility is a function of timing, having semen in the uterus when the mare ovulates, not how many times she is bred.

The four-day heat cycle you described could be an indication the mare is still in a transition, or something called a “short cycle”, which can indicate the presence of an infection in the lining of her uterus. This type of infection is termed “subclinical”, meaning there are no outward signs like a discharge, fever or lethargy. Bacterial endometritis (an infection of the lining of the uterus) is the most common cause of fertility failure. This is usually not a “venereal disease”, as mares do not have to be bred to contract it. A positive uterine culture will confirm the diagnosis and direct appropriate treatment. Left untreated, bacterial endometritis will prohibit conception and cause further damage to the uterus. Your AAEP-member veterinarian can be a great resource for diagnosing any problems your “four-day” mare may have, and help you decide the best course of action.