Breeding 25 foals doesn't make it a particularly useful herd if the remaining animals are all closely related. There's been no new imports into the herd since the original founders, and some of those never bred, so it's a very closely-related group. And likely to only become even closer since there's only one entire male left.
Some good news. The Rotterdam animals are not that well represented anywhere and the Washington stock is only bred in privately held collections in the US. So it seems a reinstated breeding programme with perhaps a new stallion would be tops for Ozzie zoos!