Bovine mammal (4)
(Other definitions for bull that I've seen before include "Animal; 23 across" , "Bovine animal" , "Slangy lies from an ox?" , "motion is > nonsense" , "rubbish" .)
(Other definitions for cow that I've seen before include "Overawe" , "Subdue the spirit" , "Intimidate; quadruped" , "Browbeat" , "Intimidate; an animal" .)