If you saw your neighbour whipping a dog, you'd be on the phone to the police immediately, right? Of course, anyone with a shred of decency condemns hurting animals. Yet, inexplicably, some still turn a blind eye to the cruelty to horses during the Grand National, in which riders are required to carry a whip. Nearly every year, racehorses sustain injuries. Many have paid with their lives.

When 40 skittish horses are jammed onto a treacherous obstacle course, viciously whipped, and forced into jumping, breakdowns are inevitable. Last year, only 17 – fewer than half – finished the Grand National, and while the race organisers were quick to highlight an absence of fatalities after last year's main event, they conveniently failed to mention that two horses died at the same course earlier in the week. According to research by Animal Aid in 2012, Aintree was the most lethal of all of Britain's racecourses, claiming the lives of six horses in just eight days of racing.

Treated like wind-up toys – their fragile limbs pushed to and sometimes beyond breaking point – many horses sustain fractured legs or necks or severed tendons, while others have heart attacks. Every year, hundreds of horses die on British racetracks. More are turned into dog food when they stop winning.

The mindset that horses are little more than tools to be used, abused and discarded is entrenched in the racing industry. Ruby Walsh's comment that horses are "replaceable" is deeply offensive. Horses are not unfeeling – they experience joy, anxiety, fear and affection. They are also clever and perceptive, as anyone who has seen a horse figure out how to open stable-door latches will tell you. However, Walsh's comments were prophetic: the very next day, two more horses died on the Cheltenham track.

Horses are sometimes drugged to mask pain and keep them running when they should be resting or receiving treatment. Raced too young and too hard, when their bones are not up to the pounding and stress, horses used in racing endure injuries, lameness and exhaustion. Last year, Godolphin trainer Mahmood al-Zarooni was banned from racing for eight years after being found guilty of doping offences.

People who care about horses should turn their backs on the Grand National and every other race in which horses are being run to death. This cruelty will end only when the public realises that there is no such thing as a "harmless flutter" when it comes to funding the cruel and exploitative horse-racing industry.

• This article was amended on 4 April and 22 April 2014 to correct a suggestion of motive behind horse racing. It was further amended on 16 April and 22 April 2014 to amend references to horse deaths and injuries in Grand National races, the fate of racehorses when they stop winning and the use of drugs and to remove a reference to "premeditated" cruelty.