The Grand National meeting at England's Aintree Racecourse started in the worst possible fashion on Thursday when four horses—Strong Promise, Lake Kariba, Rossell Island, and Architect—died during the course of the racecard. Two other horses, Bounce Back and Merry Path, sustained injuries the same day.

The deaths come just days after members of Animal Aid, a British humane advocacy group, attacked England's National Hunt racing, saying it was cruelty to horses. The group plans a major protest at betting parlors and Aintree when the Grand National is run on Saturday.

Sporting Life reported that Strong Promise fell and died instantly from spinal injuries during the four-horse Martell Cup Chase; Lake Kariba died of a heart attack after finishing third in the same race; Rossell Island died in a fall that injured his spine following a two-horse collision at the first fence in the Martell Fox Hunters' Chase; and Architect had to be euthanized after suffering a spinal injury in the Glenlivet Anniversary Hurdle.

Peter Webbon, the British Jockey Club's chief veterinary adviser told Sporting Life, "This is just very bad luck, you could say a statistical blip. If there is a pattern to the deaths then we will do something about it, but my gut feeling is that they were all genuine accidents."

But David Muir, Royal Society for Protection and Cruelty to Animals equine consultant, "Each of the incidents did not make sense. The course appeared to be in excellent shape beforehand and I don't know what else the management could have done.

"Regarding the National, I just hope the jockeys take it easy although I'm not saying these deaths are down to the jockeys."