 The situation was improved when the exchange of breeding animals among facilities increased genetic diversity and there was a consequent improvement in fertility, but the population experienced another genetic bottleneck when many of the horses failed to survive World War II.Only 9 of the 31 remaining horses at war's end became ancestors of the subsequent captive population, which did not return to its pre-war size until a decade later.By 1965 there were more than 130 animals spread among thirty two zoos and parks, while genetic diversity received a much-needed boost from a new source