Davenport Farm on the west side of Holland Valley (John's region) is a good location to find bulls. Using "The Furious" homeopathic allows you to kill a bull with one punch, completing the achievement easily. Kicking counts as well. If you have brass knuckles, you must kick the bull, otherwise it won't count.
If you don't want to use The Furious, try to stay on the backside of the cow as you punch to avoid receiving much damage. The "Ultimate Survivor" homeopathic can also be used to help reduce damage. However, the first option, using The Furious, is by far the simplest and fastest guaranteed way to unlock the achievement.
Go get that beef!