All domesticated species have wild ancestors, even in the cases when after domestication they have diverged enough from their ancestors to be considered as being now distinct species.
While the ancestors of horses have been hunted to extinction a long time ago, the wild cows that have existed in Europe until a few hundred years ago (a.k.a. aurochs) and the wild pigs that still exist have remained genetically close enough to their domesticated relatives that frequent interbreeding between them has happened, during the many millennia since the domesticated cows and pigs have been brought to Europe.
The chicken breeds that were previously widespread, before their replacement with the optimized modern breeds, had a behavior very similar to their distant South-Asian ancestors and they were quite capable of taking care of themselves, when given an appropriate space.
There is no relationship between vegans and industrial farming.
Nevertheless, nobody could be truly vegan centuries ago, without acquiring serious health problems. Veganism has become possible only after the development of the industrial technologies required for the production of the supplements needed to provide various essential nutrients, vitamins and minerals that either do not exist in plant food or they exist in too small quantities and which either cannot be produced by humans at all or they can be produced, but in too small quantities for ensuring a good health.
This is partially true. Let me correct that vegans faced serious health issue before the 50s when b12 source (bacteria) got discovered. They may have survived by eating dirty vegetable (without the washing, bacteria are still on the plant) but it’s very unlikely they got enough.
Veganism definition has nothing to do with industrial farming, however try ask vegans if they would have taken this way if industrial farming does not exist, you’ll make them think twice. In the circle I gather many says they would prefer eating flesh from an hunted wild animal than buying soap containing glycerin from pigs that never saw the sun.
This does not exist, chicken is a species made by and for humans. As for cows, pigs, sheeps, most horses…
Most vegan wouldn’t be vegan if industrial farming doesn’t exist.