What does a Cow add that isn't already in, existent animals could also be used for those tasks than mere adding a cow for sake of having a bovine, same with a horse. Horses are so over used in a transport role, add Equines but make them a hostile force like Rusthorses that drifters ride or something.
Megafauna inspired creatures ~ plenty of Marsupials in that lot for variance that can fill roles of Large predators
Swap Rhino for Hippo and you may be onto something