Most mares come into foal heat between 7 to 10 days after foaling. If your mare delivered her foal with no issues and she has the all clear from the vet, then foal heat breeding would be fine. If you do not want your mare to foal earlier next year than she did this year, then wait 28 to 30 days from her foal date (+ or - ) a few days and she should come into another heat cycle. Sometimes, really old or really young mares will skip heat cycles while lactating, but the norm is to have a heat every 28 days during the foaling season. If you have unlimited access to a stallion, he will be able to tell you when your mare is in heat and her behavior will tell you if she is ready to accept and stand for him or not.