In spite of the more severe life in the semi-reserves, reproduction was very good. Except one three year old mare, all mares in the age group of 3-11 years reproduced a total of 92.8% in 1989.
It can be assumed that Przewalski horses in the wild show a sharp foaling seasonality as is known for other feral horses. This changed in captivity. In the semi-reserves 85% of all foals were born in April, May, June and July with the highest birthrate in May and June. Five mares, four of them zoo-born, were responsible for foaling outside this season, for the others it happened after only one year.
It is evident that adaptation and natural selection will be necessary before this "inner clock" of reproductive physiology of the mares regulated by specific female hormones, will work again (KIRKPATRICK and TURNER, 1986). It is likely that Przewalski horses, released directly from zoos into the wild, would drop many foals outside the "correct season". VOLF (1989) mentions the early sexual ripeness of bodily unripe animals of Przewalski horses bred in zoos.
The age of reproduction decreased considerably in the 5th-10th generation in captivity as consequence of a creeping domestication. A high deathrate of foals from bodily unripe parents has to be expected when Przewalski horses are released directly from zoos into the wild.