Leuke vraag want ik heb dit kort geleden gelezen op een Amerikaans forum. Hier het antwoord:
It depends on how paranoid you are and how sensitive (nervous) your horse is. Horses have a double-walled placenta and the embryo only attaches to the mare after the 3rd month of pregnancy. That means it is fairly easy for a mare to loose her foal in these first three months.
I don't think riding her is directly a problem. But if you have a nervous mare and you show her for example, that could cause her enough stress to loose the foal. A friend of mine has a highly sensitive Warmblood with lots of TB influence and had this happen to her last year. Even though my mare is pretty quiet, I decided to only do some light trail riding for the first three months. And after that I'll stick with dressage, instead of our usual eventing, for a while. But of course first I have to get her pregnant!
Good luck with yours!