It depends on if she's had foals before, and how often. If I had a 19 year old mare who had never had a foal before, I would not consider it safe to breed her. But a 10 or 12 year old mare who never had a foal, and I was considering breeding her, I'd get the vet to check if breeding was a good idea and follow her advice. If a 19 year old had a foal every year since she was 4, I wouldn't consider it safe. But if the 19 year old started breeding at 5-6 and had like 4-6 foals in her lifetime who were all born healthy, got plenty of colostrum from her, nursed, she took good care of them, and maintained her weight and good health, I would think her health and her foal's would be fine.k, random question, and NO I don't plan on breeding my mare. How old is too old to breed? 15? 18? I recently stumbled across a 19 yr old pregnant mare, is that safe?