Okay, so there’s a little bit more information needed on this. Do you have them in pens or in breeding machines? We’re there a lot of other people on? How is your ping? How many animals did you already have, and is your area crowded with passive mobs?
Right now it could be any number of things. Mob spawning slows down a LOT if there are a lot of people on. If your internet is slow or you’re having rubber banding issues, things can go wonky when interacting with them. There are passive mob caps for areas.
If you can provide more information, then the more able we are to help you pin down the cause of your issue.