Thank you, very very very good points made and has given me a lot to think about.
My mare is 20, she will be 21 when I breed her, she is a reg Canadian Sport Horse(Belgian WB/TB cross).
If she were my horse, I'd do the culture, cytology and biopsy to see how she's holding up for conception before I tried anything. Here's an article that explains the biopsy grading: https://www.addl.purdue.edu/newslett...mmer/eeb.shtml
Anything more than a IIa and I wouldn't consider doing anything with frozen semen, and I'd start being hesitant about anything with extender in it. The higher the score and the lower your chances. I also insist that they do the cytology along with the culture because you can sometimes see something is brewing that won't show up on the culture quite yet. Some vets will try to put you off and say, "Well, let's just culture and biopsy and see how she goes.". I find another repro vet the minute they try that, it's only to get another call charge out of you and the cytology can show an impending issue before it becomes full blown.
At her age, I'd be very hesitant about using any kind of frozen semen, and I'd be prepared to get at least 3 shipments of fresh, cooled semen if you choose a stallion that is shipping from any distance and, of course, 3 vet costs as well. Since the shipping and insemination can run to WAAAY higher than the actual stud fee, I'd just be prepared with some good cash reserves before I even started. If you can find a local stallion, where you could take the mare to him, even if they collect and inseminate rather than live cover, your chances would be a lot better. If you can also find a stallion that they'll let live cover if she won't catch on the AI, then you will also maximize your chances of conception.
With a mare her age, I'd also be looking at being able to Regumate her for the duration of the pregnancy once she's safely checked in foal. It's expensive but if you can get her in foal, it'd sure be nice to keep her there. I've had vets say that you only need to Regumate up to 120 days, but I've found that in some older mares who chronically slipped their fetuses that keeping the mare on Regumate up until day 320 resulted in successfully getting a foal from a mare who chronically aborted.
"Serum progesterone levels greater than 4.0
ng/ml are generally considered to be adequate
to maintain pregnancy. Mares with
concentrations below 4.0 may be at some risk
of pregnancy loss. It is often recommended
that supplementation with RegumateŽ
either 1 to 2 days after ovulation or after
pregnancy is confirmed. Therapy is usually
continued until day 120 of pregnancy, at
which time production of progesterone by the
placenta is adequate to maintain pregnancy. "
Just some things to consider, this breeding thing is EXPENSIVE no matter how you cut it, if you aren't using your own stallion.