IRL there are various attempts to curate captive populations of once-wild animals or release the young that are not yet so totally human-habituated (
here's an interesting recent variation!), by hand-rearing chicks from hatching in a way that
aims to avoid imprinting upon humans.
I
think the way DF works is to assume that offspring of tame animals start tame, rather than neutral or perhaps even inclined to be wild (imagine the !!fun!! inherent in dorfish animal husbandry if it were not so!) and I don't think there's much scope for an Animal Untrainer in the DF era.
But 'feralising' is a suitably historic thing (unintentionally so), if a good balance can be struck between deliberate shunning the tame animal and what would happen if nobody visits the tame leopards and their offspring for years just because of the usual fortress-work cruft getting in the way. Maybe, when it's not just grazers that need enough to eat, we'll start to
really care about keeping the carnivores provided with suitable non-dorf meat (on the bone, on the hoof or on the run) of our choosing.
Perhaps full-tamed status should also rust (with
several warning opportunities, perhaps requiring a couple or more new generations to trip over the intermediate thresholds on the way to feral (not actively dangerous to fort-population creatures, but no longer trainable or happy to stay pastured without bringing in the Trainer or other sustained contact again) and offspring of feral creatures that change from infant to adult without positive interactions from civilised creatures can become fully wild.