The common thought that the Red River Ox Carts were pulled by fitting a horse collar upside down onto the ox seems at least partially in error. True, they resembled horse collars more than they did ox yokes, but from the old photos below I have concluded they were tailored for use on oxen.
On the left is the clobber which rode over the ox's back to support the weight of the cart. On the right is the collar which is constructed of two pieces of wood. These two pieces are covered with leather on one side only; this single piece of leather also bridges the top of the neck, effectively attatching the two halves of the collar together. The bottoms of the two halves are notched in such a way that it appears the ends must have been lashed together at the throat with a narrow leather strip or rope. This would have allowed placement and removal of the collar.
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One leather strap goes from the clobber to the cart shafts (providing lift); another goes from the collar (providing tug).
An old photo (not included here) appears to show a belly strap on the clobber, while other photos do not. They all show breeching straps around the ox's backside to hold everything in place on the downhill slope.
This photo shows the leather covered side of the wooden collar draped over a cart wheel.
