Personally, no. There are practical reason for foal heat in the wild (cleansing, preventing late year foals, preparing the body for subsequent cycles). I personally have waited one month the one time I bred my mare 2 years in a row. Who's to know most wild mares settle on foal heat? Having given birth twice myself... I'll give her a month at least. There are other factors to consider, such as age, delivery complications, recovery. Wild horses have a savage existence, but we are stewards of our mares. I wouldn't personally breed a mare on foal heat but I'm sure many do fine.