You won't know until she gets pregnant and puts a live foal on the ground. However, as Kyzteke said there are things you can do to get a good idea of your chances of success. Have a complete repro exam done; this usually involves an exam with a speculum to view the cervix etc. Have an ultrasound done to check for anything funky; cysts, fluid, non-functional or otherwise abnormal ovaries. Have a culture/cytology done to check for infection. Have a uterine biopsy done to check for inflammation/fibrosis. The biopsy will give you a "grade" which gives you a broad range of % of whether the mare WILL CARRY TO TERM. None of these tests is a guarantee, but they can go a long way in giving you an idea of just what you are dealing with.
Or you could just buy a mare that is already in foal and skip some of that !
Buy a proven mare. I tried 2, one for 1 year one for 2 years (both took but didn't carry longer than 60 days). Everything said there shouldn't be a problem, but with 2 different repro vets, no foals. Started over with a proven broodmare
Irish Draughts and Irish Draught Sport horses
I'm with Touchstone - buy her in foal! I've got two mares right now that have absolutely NOTHING wrong with them, clean C & C, clean ultrasound, both have easy breeder dams, both have clean, normal ultrasounds, both cycle normally, and one even had ONE foal - I got hold of the breeder who finally admitted they had a heck of a time getting her in foal, which is why they finally sold her I sent one of them off for several months two years ago with a repro specialist who finally threw up her hands and said "good luck, try a live cover and see if that works". We've labeled these girls the "freeloaders".
It is hard for breeders who buy mares with performance careers (which is what I did) as broodies, buying bloodline and performance results.
Well, as we all know, just because they conceive doesn't mean they will carry to term and deliver a live, healthy foal. The breeding world is littered with mares who will conceive but not maintain the pregnancy. So buying one in foal is only half the deal.
If you are buying the mare to be a "life time" broodie, you are better off getting a PROVEN broodie....there are plenty out there for cheap these days.
If you are buying the mare mainly to ride but MIGHT want to breed her some day, you are better off just buying a foal already on the ground...support all us starving breeders <g>!
I have a young mare who does not cycle. She has teeny, tiny ovaries and makes almost no hormones necessary to cycle. She is a lovely, small TB with great breeding so I was going to breed her to ponies. She is now being turned into a small hunter -- no mare issues for this one -- I guess that is marketable
If buying a young mare (under 2yrs old) I'm not sure one would want to risk a full bore repro exam.
If the mare is 3yr old or older you can of course do a full repro exam. But make sure a vet isn't taking you for a ride on the involvement of the exam.
I had a vet out once who wanted to break the hymen on a maiden mare to culture. HaHaHa!!
If you're buying a young broodmare prospect from a breeder - you can inquire about the fertility of her dam and grand-dam if the breeder had them both for a while. That would be a pretty good indicator as well.
If you look to the cattle industry you will see lots of studies and practices that they look for fertility. Reproductive health is partially genetic and partially environmental.
Breeders don't usually have good cause to leave a broodmare barren for years or every other year. So you can look at the consecutive years her dam carried full term foals.
Assuming a young mare hasn't had any 'violations' to her anatomy or infections a basic repro exam where a vet examines the tone and internal anatomy of the mare should be sufficient.
I have bought youngsters on a palpation that they have all their "parts" and have done fine. But if you buy an older mare from a breeder, well she is for sale for a reason most likely.
Unless someone is getting out of the business, or trying to keep x number of mares breedable to their own stallion. If the sale mare has had foals every year and a decent biopsy you are probably ok.
You can't until she has a foal. And that just proves she got pregnant and foaled successfully for someone else and still might not for you.
I poured in incredible amounts of effort and money trying to get a foal from my Pregelstrand mare, my first Trakehner. Nope, nope, nope, nope, $$$$, and nope. I finally gave up with her, bought another to be my foundation broodmare, and rode the first mare instead. She and I both were much happier. But she had had all the tests, biopsies, etc. There was no reason, except that she was not going to have a successful foal for me. Awesome riding horse, though.
Well, there are no guarantees in life but death and taxes... but their are some indicators that indicate breeding soundness.
Obviously a good repo exam is invaluable. Having had foals successfully is another indicator, but it's important to know how she was bred. If a mare has a foal in September (in the northern hemisphere), then it's a good bet it took quite a bit to get her bred that season(for instance). Other ?s to know would be was it live cover, was she "cycled" artificially (under lights or with other treatments), did she require any medications? If it was by A.I, how many doses did it take and what was the fertility like on the stallion?
One thing that many types of breeders (besides horse breeders) take very seriously is the fertility and mothering ability of the females in the herd (sheep, cattle, goats). Not only do they usually use the females that can get pregnant easily, carry to term, and keep the baby alive til weaning, but they also usually use the males from females that can do that. Horse breeders will try a lot harder to get a foal from a mare than other types of breeders will (for better or for worse). Many types of breeders have found that mothering and productivity is passed very strongly on the female side (but they don't discount the sire's dam either). Look at the dam line, and the sire's damline. If their are mares that have produced a lot of foals (and especially back before artificial means were used) it can indicate a likelihood that a mare or filly will be productive as well. There are some damlines (in all breeds) that are very profolic, and it's usually because the root dam had a lot of foals, and those foals produced a lot of foals. (in Arabians Rodania and Wadduda would be one of them, they share the same damline, which was finally found through DNA testing, and both are very widespread damlines.. because the mares through the last 100+ years have had fillies that produce just like those two mares did.. easily and every year).
I bought two mares in their teens that never had foals before. One of them was a big risk. The former owner had tried three years in a row to get her in foal. Her chances were very thin but she was so beautiful and a good mover that I could not resist and bought her anyway. I really wanted to have a foal just like her.
She had the entire test perfect; there was no reason not to get in foal. She was sent to a specialist in repro and stayed all spring and summer, $$$$$ for nothing. In fact both mares were sent there with no result. But I had used frozen semen which might not have helped.
Last year I prepared them. Flax, immunal and fresh semen. My favorite mare got in foal on the first try!!! I was ecstatic. It did not work for the second one until I decided to sell her. The day before she was going for a try out to a very interested party, I had her checked ‘just in case' but with no expectation at all. Ooops! I think this time she got scared and she knew it was her last chance if she wanted to stay! They should have their babies this spring.
It worked out but I would not take that path again...I guess. Hum
Probably a lot to do with frozen. For harder to conceive mares (depending on why), usually live cover is best, with fresh shortly there after. Frozen just doesn't seem to work as well on maidens or difficult mares.