A harness is rigged to be attached to all the deer, and swing with their running motion, even if you manually change the deers' positions.
The model and materials are not intended for close-up renders, but for totals of the sleigh and the deer wooshing across the sky. One texture file is included for the deer, the rest of the materials are simlpe Max materials with procedural maps like noise and falloff.
If you have your own hi-res sleigh model, you can attach it and still use this rig.
View the attached video clip for a full demonstration.