A simple two horse trailer will be about 2500 lbs empty and each horse will weigh about 1000 lbs. That puts the tongue weight at 500-700 lbs. Although many new receivers have a higher rating than this for dead carry weight, this changes quickly once you use an extension and increase the leverage. If you read some of the warnings on basic extensions, they state they are not to be used with weight distributing hitches. I suggest the OP uses the information presented to find a safe way to haul his horses - I have no doubt there is more than one to do this safely if you factor in weights and applied forces.
imwildfire: I'm glad you had powerful engines in your trucks out in the flatter Midwest and were able to tow your horses successfully. The truth is that there were plenty of small block V8's available with as little as 120 hp in the 60's and 70's. I never advocated towing bellow safe speeds on highways. Most people that towed slowly were smart enough to stay on the secondary routes which allowed them to make it to their destinations safely. Today you see people with heavier loads cresting 7000-8000' passes at freeway speeds - The hitch required for panic situations has to be designed heavier than those that took the slow road.
