I spoke to our abbatoir the other day, and they were more concerned about the animals welfare than about loading gates. They were happy for us to take two orphan lambs from last year to them in the back half of our transit van. If we had put them in our trailer, we would have had two smallish sheep rattling around in a 8ft by 5ft trailer, instead of nice snug 4 ft square space in the van.
Speak to your abbatoir and see what they say.
Beth