There are regs for the exact angle of the ramp slope, and for space inside - they need enough so they're not crowded but not so much that they rattle around. If there are not enough animals to prevent themselves being flung around, then you may need to sub-divide the interior. The space each sheep needs is laid down in the regs, and is part of the test of competency you need to transport animals more than 50 km. There must also be correct ventilation and so on.