Horse Breeding:
Frequently Asked Questions
How long is the mare’s heat cycle?
Mares have a 21 day cycle (similar to how humans have, on average, a 28 day cycle). During that time period, there will be 1-3 “good” days for breeding. We can use medications to narrow the breeding “window,” but there are times in which a mare’s cycle is irregular and we can’t breed her on schedule.
How old is too old to breed my mare?
This depends on a lot of factors! If your mare has never delivered a foal (she’s a “maiden”), we may start to encounter problems with breeding her in her mid-to-late teens. The biggest problem we see in these mares is a cervix that fails to dilate properly during the heat cycle. This can make getting her in foal more difficult and costly, because fluid and inflammation can accumulate inside the uterus. If she does get pregnant, the cervix will open for foaling, so you don’t have to worry about that. Mares who have donated embryos, but have never carried and delivered, would still be considered a maiden in this circumstance.
An older mare who has had foals regularly will usually be able to continue getting in foal until she is in her mid twenties.
A mare in her late teens or early twenties, who has had foals, but not in the last 3-5 years, may fall in either category. Most of the time, we just won’t know how your mare will handle being bred until we try!
Can I transfer an embryo from my mare into this other mare I have?
Well, that depends on a lot of factors! Choosing a recipient mare is pretty much the most important part of an embryo transfer. Often, the best option for embryo transfer is to flush the embryo from the donor mare, and ship it to be placed in a “professional” recipient mare at a large facility. If you choose this option, the recipient is shipped to you once she’s in foal, or the foal can be shipped to you after weaning.
If you do want to use the mare you have on-hand, we strongly recommend that she be between 4-15 years of age, of good size, of good temperament, body condition score of about 6/9, have had at least one foal (preferably within the last three years), and have good vulvar conformation. If she passes the initial “screening” of that list, then she should have a uterine culture/cytology, biopsy, and a vaginal speculum exam to confirm that she’s a good candidate to keep that valuable embryo safe!
When multiple recipient mares are available (like a large herd), the “best” mare will be chosen to receive the embryo on the day of transfer. When we have a single recipient mare, we’re dependent on administration of drugs and hormones to create a reasonable uterine environment for the embryo.
You should plan to spend an extra 2,000-3,000 if you want to use your own recipient mare! This will usually be equally, or more expensive than choosing to ship your embryo.
Can you come breed my mare this week?
Probably not! Like humans (and all other mammals), horses are only fertile during a small window in their cycle! Many times, people think that I can simply show up and inseminate their mare, but the chances of us randomly picking a fertile day out of a three-week cycle is very, very slim! In addition, many times we evaluate a mare and find that she has a problem that needs to be addressed before she is likely to be able to carry a foal.