Pig
Pigs were added with the first version of Survival Test. They spawn in the daylight, like the other friendly mobs, in groups of 1-4. They wander aimlessly until killed. In Survival mode, on death they drop a raw porkchop. Since Indev and onward they drop 0-2 units of pork. In the most recent build of Minecraft, they eat mushrooms when they walk over them. Friendly Mobs are also known to jump on top of torches, which makes them susceptible to simple traps. If you set a pig on fire with flint and steel he drops cooked pork.
As of the 1.5 Beta update, lightning during a thunderstorm may hit a pig and transform them into a zombie pigman. Normally, zombie pigman can only be found in the Nether, but now it can also exist in the normal world.
As a result of frequent prodding from a user known as Miclee, Notch added saddles for the pigs during a Secret Friday Update. The player is not able to control the pig while riding it, however it does protect the player from fall damage. Pigs drop meat when killed, which can be eaten raw for 1.5 hearts or cooked for 4 hearts. Pigs can also be ridden with a saddle, that can be only found on spawners chests.
Pig (Status Card) Health: 5 Hearts Drops: 0-3 pork pieces at once Color: Pink
Side Note: Pigs love to push people into lava.
Sheep
Sheep were added in the first version of Survival test. They spawn in daylight and are generally in large groups. Sheep wander aimlessly until killed. Hitting a sheep once with shears makes them drop 0 to 3 units of Wool (which regrow, literally, over night), and attacking beyond that will kill the sheep, yielding nothing upon death. In the latest version of Indev, sheep eat grass, but in Minecraft infdev and onward they do not. Sheep with black and gray wool have been added in the 1.2 beta update on January 13th. Brown and pink sheep were also added in the Beta 1.4 update, on March 29th. The 1.2 update also let players dye sheep a variety of colors. Pink and brown wool is considered rare, so to find a brown or pink sheep is extremely lucky. In beta 1.5, sheep can now be found in most natural colors, including brown, tan, black, pink, yellow, and gray
Cows
Cows were added with the 1.0.8 patch on July 20, 2010. Cows spawn in daylight in groups of up to six. As with pigs and sheep, they currently only spawn on grass. Killing cattle produces 0 to 2 units of Leather. Milk was also added in 1.0.8, and in 1.0.11 players could right-click a cow with abucket to obtain milk. You need milk in order to make cake.