Oh yeah cows are right up there with ponies when it comes to things that will eat horses!!
One of the horses I'm riding at the moment doesn't like cows that much but its when the little ponies come running that she FREAKS!
She hits the breaks and looks at them as if to say:
"WHAT THE HELL IS IT?!!!"
Then she bolts and if she could talk then she'd be yelling "Evil mutant ninja ponies! RUN!!"