Farm animals are not pets and can be dangerous. You should not walk up close to an animal unless you are with an adult who is used to dealing with it. The animal might get nervous and kick you.
Bulls can be ready to attack at any time, so you should never take a chance with them.
A cow that has just had a calf is ready to attack anyone who comes near, so you should keep away.
If you do walk up to an animal, make sure it can see you. If the animal can't see you, it will most likely kick out at you.
If cattle are bellowing loudly - they are in some kind of pain, or afraid, and they might attack you.
If cattle are pawing the ground, keep away. They might be getting ready to attack.
It is really important to wash your hands well with soap and water after handling farm animals.
Source: AgriKids Farm Safety Supplement, Western People.