Pets use same map as dwarves. Pet blocking but passable doors then has them endlessly trying to path through the door and failing. This will kill your FPS.
Training by any trainer doesn't help in my experience. Doggie pack going after your trainer will eat into your FPS.
If you cage all these pet cats and dogs you can minimize their FPS impact (there will be still some counters associated with them, though)*
Also, for breeding the males have able to meet up in adjacent squares. Not sure how that works with egg laying, though.
*Hm, got a fun if pointless idea: embark with 7 puppies, war-train them and assign them as pets once they grow up, then stuff in a cage in meeting room to give your expedition founders happy thoughts about seeing their own pet?
The ones pathing through doors arent pets, its farm animals, the pets are just choking my meeting hall, but the farm animals have had a blue ! over their head for better part of a year, only ones impacted is one of 4 wild boars, and 3 of my 6 elkbirds (im basically giving up on them, securing a supply of horn isnt worth this much of a pain in the ass, and ive never even run into the problem about them people complain about, they wont even claim nest boxes, and those that do are all infertile, no matter how many males are around) and will not stay in pastures, dwarves come, return them to pasture, second they are let go, they sprint back to the door and stack up on it, so the dwarf leaving releases all of them that were brought back, creating several more pasturing jobs, for which the same thing happens.
They are pastured in that pasture, they do not have nest boxes somewhere else or anything like that, im about ready to just stick every grazer in a cage, and either let them die or try and build an area blocked by raising bridge to stuff them in, hope the game wont also make them path as though they could walk through walls.
I just wish the game was that tiny bit more helpful and actually told you what was wrong, why are they "overcome by terror"? nothing is attacking them, nothing is after them, they have food, the pasture is huge, they have never had children, so they cant be like upset that their children are taken away, if such a thing is even in game. Nope, all I know is "overcome by terror" and that it manifests itself in an all consuming desire to path through doors ive locked against animals, if I -dont- pet lock them, they just scatter at random around the map, if they are locked, they obsessively run through all of them them for no reason before escaping and running all around the fort.