Just to put the statistic linked to by mathanxiety above into some sort of context, approximately 6,600 horses (a conservative estimate) will have run in the Grand National since 1839. Those 79 deaths listed are incredibly sad and every racing/horse/animal lover wishes they hadn't happened, but almost 99% of all GN runners came home safely.
10,391 animals are used in animal experiments / testing / vivisection in the UK every day.
370 animals are rescued from cruelty by the RSPCA* in the UK every day.
19 stray dogs are put down in the UK every day.
27 cats or dogs are hit by cars in the UK every day.
Almost 2.5 million poultry birds are slaughtered for food in the UK every day.
Approximately 82,000 cattle, sheep and pigs are slaughtered for food in the UK every day.
I think of (and in some cases see first-hand) the conditions these animals live in, and in many cases the manner of their deaths, and I just can't reconcile the pampered lifestyle of racehorses who get best of food, bedding, rugs, veterinary attention, regular exercise, companionship of other members of their species etc etc as "abuse", even if on regrettable occasions that life is cut short on the racetrack, where death comes swiftly - either instantaneously or within minutes at the hands of a trained vet. Death is not the worst thing that can happen to an animal.
*RSPCA figures only; does not include any other UK charities / rescues / shelters.