So, I’ve been slowly looking into doing a re-breeding of the filly I lost. The hope of having something even remotely like her to bring along has been helping me deal. While I do have a lovely gelding from the sire, I really want a filly from this cross. I asked my vet about the possibility of sexing the semen, but he said it wasn’t possible because we only have frozen on my guy. I just did a little bit of research that said they’ve been sexing both fresh and frozen semen in bovines for awhile now, but I couldn’t really find anything on equines. My mare is 12, and while I love her babies, I love riding and competing her more so I don’t want to keep trying over and over and over again to get a filly. Any thoughts or information? I’ve looked all over the web and can’t seem to find anything conclusive. BTW, the mare is extremely fertile. She has only been bred with frozen and has caught on the first try both times.
I believe you can sex semen, but I have been told it must be done before freezing. Could be wrong though.
My sister is the head veterinarian at SexingTechnologies.com They sex bull semen and other semen. 
If you like, please send me a private message and i will give you her email address and you can ask her directly.
Thank you. The whole reason I decided to ask is because there was a website that said they offered sexing for semen that had been frozen before. Granted, it was for bulls, but they mentioned reverse sorting. I know when I was in college we mostly worked with bull semen with maybe some boar semen as well, so I can’t speak to why this wouldn’t work with equines. Guess I should go rummage in some boxes and find my old repro notes. I’ll send you a PM 
‘Sex-sorted’ bull semen, which we use successfully, is centrifuged (spun quickly), leveraging the weight difference between male and female chromosomes in the semen. It is not a perfect science, in that it gives a 90% chance of accurately determining sex.
The process also measurably reduces efficacy and fertility of the semen.
Cattle repro is much more robust than equine, and also much further advanced in its R&D. Everyone needs to eat. Not everyone needs a horse.
Advances have occurred in equine repro, such as ICSI and the ability to freeze, thaw, then successfully implant embryos. To date, however, my understanding is that there is no commercially proven equine equivalent to this bovine practice. Furthermore, you seem to want to sex-select from existing frozen. This would be much more fickle again, as the more you mess with the process, the lower the fertility becomes.
