If you are at 500', and I looked at your EXIF and you shot at F/8 your Depth Of Field would have 147' by the calculator.
At 400' your DOF would be 93.6'.
Knowing the average size of deer and the framing it looks to me like you are about 450' away.

You should have enough area in focus at that distance to cover the deer. Your lens would have to be way off.

Also use RAW format, the files from the t4i should sharpen nicely. If you are using JPEG you are losing out on that advantage.