Minecraft wiki entry for Horse_Update, associated text: Resource packs, which replace texture packs.
Item and entity attributes.
3 new status effects: Health Boost, Absorption, and Saturation
2 new commands and 2 new sub-commands to /gamerule
Horses and their variants.
5 new blocks: hay bale, carpet, block of coal, hardened clay, and stained clay (the last two are now terracotta)
4 new items: horse armor, horse spawn egg, lead, and name tag