Horses on the Pampas

Wild horse population growth rates are largely driven by mare numbers, reproductive rates and mortality.  Would the large numbers of free-roaming horses in historic accounts have been at all possible starting from the small numbers of mares brought to the continental Americas?

In year Mendoza reportedly released 7-12 horses when the Spaniards left Buenos Aires (Nichols, 1939 and Gregson, 1969).  Assuming it was 11 3-year-old mares and a single 17-year-old stallion, assuming the mares has a live foal every year between age 3 and with a 50/50 sex ratio and that all horses died at age 21 and not before, it would take 24-25 seasons to reach 10,000 feral horses.

There were numerous importations to the Pacific edge of South America.  Indigenous populations in that region had experience with transportation sized animals in the form of the native camelids.  It is possible that the equine population expansion relied at least partially on animals from those importations augmenting stock that remained in Argentina if any.