Can you breed a small mare to a larger stallion?

I've looked into this question. Depends on the size difference and the willingness of the mare, but if she is winking, etc., many times the mare will lie down or crouch to allow the smaller stallion to mate. As for the foal size and reaching to nurse, there was a study done in England in which shetland fertilized eggs were placed into draft horse mares, and the other way around. Unique to horses, the mare's uterus has hormones which control the size AT BIRTH of the foal. So a shetland mare's foaling of the draft horse baby (which had been implanted) was not impossible because her uterus kept the baby small (and he later made up the difference by growth spurts to catch up to his true size). Similarly, the draft mare's foal was larger than usual for a shetland foal. So, if you have a 14-15 hand mare, it is theoretically possible that the foal will be able to reach. Nature is against it working, both at conception and after birth but it has been known to happen.