Cow

Cows are passive mobs, and have brown skin with white spots. They are the only source of leather, raw beef, and milk. They are 1.6875 blocks tall, 0.625 blocks wide, and 1.5 blocks long.

Behavior
Cows roam in the Overworld, usually in herds of 4 to 10. They tend to walk around aimlessly, mooing, but they will flee and jump wildly if attacked. They seem to walk slower as of 1.2. Cows make no attempt to stay out of water. Cows will follow the player when holding wheat, which is used for breeding (see Breeding).

A cow can be milked by right clicking the cow with an empty bucket. A cow may be milked an unlimited number of times with one bucket.

Breeding
Breeding Cows with wheat will create a Calf. The parent Cows have a delay of five minutes until they can breed again. Parent Cows will follow the Calf until it is fully grown.

Calves will move faster and takes 20 minutes for it to fully grow. They do not drop anything when killed. They can be milked, however.

It is possible to herd cows along with any other animal if you simply walk by a cow while holding wheat. The cow will follow you where ever you go. You can do this to lead animals into fenced areas allowing easy breeding.

Farming
Creating a colony of Cows in an enclosed area and breeding them is a way to ensure that the player can get an unlimited supply of steak, milk and leather.

History
Cows were introduced in Alpha 1.0.8. When killed, they dropped only leather, and could be milked.

In Beta 1.8, cows flee and jump wildly if attacked.

Since 12w07a, Cows have the new AI system. 

Trivia

 * Cows in the PC Gamer Demo of Minecraft are branded with a 'PCG' logo on their side.
 * In SMP, clicking anywhere on the Cow with a bucket will fill it with milk, but only at the maximum distance at which you can use the bucket.
 * Because of the lack of hierarchy in every box model, the horns of the cow are sometimes misplaced. Jeb is planning to fix this.
 * All cows in Minecraft are actually females.
 * Before Alpha 1.0.14, Cows were dark grey and had no horns: