It's interesting that people who are concerned about thoroughbreds don't seem to care about the many unwanted horses and ponies which are killed/culled or die via neglect each year. Or those in developing countries which are litterally worked until they drop (I know their owners have much harder lives than I can imagine).
In the past, I've volunteered for an organisation that tries to give unwanted dartmoor ponies/ponies off the moor a future. These ponies are esentially valueless (unlike thoroughbreds) but more are born every year due to the way the herds are managed. Many animals are culled each year for no purpose, and some sadly die through neglect. Many will suffer during the winter, when no additional food is provided for them (as they have no value) or suffer due to lack of vet treatment.
I really hope some of the people on this thread who are concerned about horse welfare would be willing to donate some money or time to a local horse welfare organisation. Sadly many rehoming centres are overflowing at this time- there is a leisure horse breeding crisis in the uk and many people also had to give up there horses at short notice during the recession. More and more horses are also being dumped on common land.
Alternatively, please consider donating to one of the many wonderful charities which help working equids (and their owners) around the world. Many of these owners are very poor, so charities are the only way of ensuring these horse recieve, for example, veterinary treatment which helps prevent suffering.
I don't think the grand national is perfect- although I do think some of the recent changes (e.g. moving the start, changing the fence structure) seem to have made a positive difference, although after only two races in reasonable conditions it is really too soon to tell.
If I had the power to, I would reduce the number of horses racing to 20- which I think would make a massive difference to the safety of the race, especially at the start. I would also not allow the race to go ahead in really awful weather conditions or very heavy ground, which is when there tends to be the most fallers, fatalities and jockey injuries. However, I do accept that these proposals can be difficult to carry out in real life. That is the thing about being involved in animal welfare- you have to live in the real world and interact with what is possible (For example I think many animals should not be kept in zoos but accept this is needed for conservation reasons).
I also think there is probably some cruelty in racing. That is because I cannot think of any sphere involving animals where some cruelty is not involved. However, at least most in the racing industry are knowledgable about the animals they are looking after, and can ensure they recieve the very best of care. This is not imo true of a very many other animal settings.