I have created an identical world in both version 1.7.10 as well as snapshot 14w32d. Both on creative mode. It would seem that the new rabbits have taken the place of almost all horses in this seed. Horses now seem to be very rare and almost non existent. I encourage you to look in as many plains as possible to see how widespread this seems.

Here is the seed I used: 1630353705672252276

Here are the coordinates of a plains biome to verify this: x: 968 Y:72 Z:-255

Screenshots attached.