It probably varies by animal and several other factors. I know that some dogs can not even give birth vaginally because they have been bred to have such huge heads compared to mom’s vagina. I watched my Dalmatian many years deliver something like 11 puppies and she did not show any sign of discomfort on some of them (they just slid out while she was busy cleaning up the pups and the surrounding) but maybe the first was difficult and by the last ones she was exhausted. So I would guess it is highly variable dep
