Basically, I started a single-player map for the pre-release. I then used the spawn horse egg a whole bunch and placed randomly facing blocks of Hay down around the horses. After a moment, a few of the baby horses began suffocating, I turned around to find their skin was red as if they were taking damage, but it appeared as if they were colliding inside the solid hay block and suffocating. Rarely, they would get out on their own. Most of the time, they just started suffocating and died in mass quantities.
1. Play 13w22a or 13w23a
2. Start a single player map, Creative.
3. Spawn a bunch of horses. You will want the baby ones.
4. Place several hay blocks near by them.
5. Watch the baby horses die painfully gruesome deaths as they suffocate on straws of hay. Obviously they live very sad lives and have nothing left to live for. They must be that afraid of Steve that they would rather commit suicide than grow up into adult horses and live happy lives with other adult horses.