Minecraft wiki entry for Cow, associated text: 0–2 leather. The maximum amount is increased by 1 per level of Looting, for a maximum of 5 with Looting III.
1–3 raw beef (or steak if killed while on fire). The maximum amount is increased by 1 per level of Looting, for a maximum of 6 with Looting III.
1–3 experience orbs are dropped when killed by a player or tamed wolf.
1–7 experience orbs upon successful breeding.