The Channel 4 program, How to Win the Grand National, is still on 4OD. It is well worth a watch no matter what you think of horse racing.
I expect it will add weight to both sides of the arguement. Most here seem to have made up their mind despite not bothering to find out if their reasoning is actually accurate or not. For example, in it there is clear evidence that thoroughbred horses' legs are indeed extremely well equipped to jump large obstacles, and as herd animals, when left to their own devices will run together, race each other and jump things without influence from humans, perhaps because it is naturally what they enjoy doing.