Quote Originally Posted by TinCow View Post
FYI, I went exploring for some horse and also failed to find any. However, I've been doing some googling and it appears that they take some work to spawn in existing (pre-1.6) biomes. Apparently you need to just run around a plains area and slaughter every passive mob you see. If you kill enough of the things eventually horses may spawn. I have not tried this yet, but the internet says it is true and when has the internet ever been wrong about anything?
That's what I have been doing north of my castle with no luck... pigs and chickens seems to spawn back though - there are always pigs and chickens there when I go hunting.
[edit] I ran around some plains biomes slaughtering everything and had no luck. The internet suggests using fence to enclose as large an area of plains as possible, then lighting the entire area with torches and slaughtering everything inside until horses appear. Apparently passive mob spawning rare are very low, and horses are rare even within passive mobs, so it can take a very long time for them to appear even if you've slaughtered the passive mobs to keep it under the spawn cap.
I haven't tried this yet...