 Many facilities failed in their attempts at captive breeding, but a few programs were established.However, by the mid-1930s, inbreeding had caused reduced fertility and the captive population experienced a genetic bottleneck, with the surviving captive breeding stock descended from only 11 of the founder captives.In addition, in at least one instance the progeny of interbreeding with a domestic horse was bred back into the captive Przewalski's horse population, though recent studies have shown only minimal genetic contribution of this domestic horse to the captive population.