Cows come in herds. A herd of cattle is a dangerous entity to a wolf. Even domestic cows will kill a wolf.
Oh, yea! Like the buffalo herds in Yellow Stone. That must be why wolves don't eat the buffalo, they fight back.
(I do get your point. Cattle in herds may not be "an easy" kill as I supposed when compared to wild boar. It's a fair point. Chickens and goats on the other hand....) ;o)