Minecraft wiki entry for Nether_survival, associated text: Cows, pigs and sheep can be brought through the portal, which can provide you with wool, leather, and meat. Sheep require special measures: You'll need to get a grass block with a Silk touch tool or killing an Enderman holding one and use that to start grass on a well-lit dirt floor, so they can regrow their wool. You can also just breed the sheep until you have a lot, and then shear some of them and kill the sheared ones. However, the sheep do not re-grow their wool.