Will the new animals spawn in already generated areas?

[Jesse Hobbs]

I just updated to 1.19 and I'm not sure if the new animals will spawn where I've already been on my current world.

[Maelstrom]

Probably not. 

But someone else with better understanding of world gen and animal spawn points may provide a more reliable answer.

[redram]

As I understand it (and I am not a coder) they should, yes.  The game does an initial spawn check when a chunk is first generated.  But then, over time, it will backfill in mobs into appropriate-condition chunks.  That is my understanding of the nuts and bolts behind it.  The backfill can be rather slow though from what I understand, so it's probably most likely to happen in chunks you spend a lot of time around, like near your base.  Note that goats have pretty specific spawn conditions, mostly involving rather high altitudes, so they can be a bit tricky to find even in fresh chunks.