Many years ago we used a two horse trailer for a couple of cows. We took out the center divider and it worked pretty well until one of the cows got excited and climbed into the manger and broke through the floor of the manger and was seriously hung up. It's amazing what a small space a 1100 lb cow can get into with enough incentive.
Horse trailers typically cost more then stock trailers of the same general size. You can safely haul horses in a stock trailer but not necesarrily the other way around. It would work fine for little calves, but they have a tendency to grow and get too big too fast.
We use both a 2 horse rear load trailer and a "combo" trailer for hauling our Longhorns as well as horses (but not at same time). The 2 horse trailer can haul ONE adult cow or bull...works fine; or, to haul 2 calves.
The Combo trailer has center divider and we can haull 1 or 2 in each section, depending on their size. Can haul one cow and her nursing calf in each section.
Have used this system hauling Lo0nghorns 4-6 hours to a show with no problems, as well as hauling one or 2 same distance. Helps to give them a flake or two of hau to munch on while they are traveling--keeps their mind off other things.
Another thought. BEFORE you borrow or rent a trailer from a private individual, be sure the wheel bearings are checked and packed properly. Also, hitch is in good working order as well as lights. Borrowed trailers have been known to breakdown when YOU have them...lol.
We use a 2 horse trailer, bought it because the price was right. It is a larger trailer (I have seen small ones). Took out the dividers, the floor is in good shape and it has worked well for us. We have hauled two animals to the processor in it for the last few years (they weighed about 1300-1400lbs) with no problem.
would have prefered a stock trailer, but again this one was the right price and its worked out fine. donna