Unless Mojang changed it back, once you kill the animal or the animal dies it doesn't re-spawn any more. You can only FIND animals they won't spawn near you. Once you have two of the same animals you can now breed them by having a certain food in your hand and right clicking on both of them.
Just do a little exploring and you should be able to find them. Some animals like the wolf and such are harder to find sometimes.
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Used a mod or put grass in your house dirt doesn't work so you need to find grass surrounding that dirt you placed and then you need to wait till the dirt goes to grass. Animals only spawn near grass.
U need to make saddles
You don't need a texture pack to have better grass. You can download McPatcher at minecraftdl.com
You don't need to feed sheep anything to keep them alive, but they need wheat to reproduce. They also eat grass after you shear them to restore their coat.
It's the default mode of minecraft, you need to collect your own resources and hunt animals to get food to feed yourself.