An investigation has been launched after four horses died at Musselburgh racecourse on Monday.

The British Horseracing Authority (BHA) will review what may have led to the deaths of Smart Ruler, Leather Belly, Sierra Oscar and Kensukes Kingdom at the Edinburgh racecourse on Monday, with one seemingly related to a “sudden collapse”.

Bill Farnsworth, the racecourse’s general manager, said: “Our thoughts are with the owners, trainers and stable staff of these horses.”

He added the ground conditions and weather “were ideal for racing but until we have further information it would be wrong to speculate”.

Inspectors are due at the racecourse in the coming days and some of the horses are also being sent for post-mortems.

Robin Mounsey, BHA head of media, added: “The incidents at Musselburgh were extremely distressing for everyone involved in the sport, not least for the owners of the horses and the trainers and stable staff who cared for them through their lives.”

As the sport’s independent regulator, the BHA said it “obviously treat issues such as this very seriously”.

According to charity Animal Aid, the winner of the day’s first race Kensukes Kingdom was badly lame at the finish and was later destroyed.

As the afternoon progressed a further three horses died in the space of 90 minutes.

Smart Ruler was seen to suddenly drop away from the other runners and collapse.

Sierra Oscar was seen to pull up with a broken leg, and was also destroyed.

Leather Belly was running on the final bend of the race when he also broke a leg during his second race.

A total of 182 horses have died this year across in the UK – all as a result of racing.

Claire Bass, Humane Society International UK executive director: “The latest tragedy in Musselburgh that saw four horses lose their lives in just one day has surely got to signal that we need to radically reassess what we subject animals to for our entertainment.

“Horse racing isn’t simply about a harmless flutter, it so often means pushing horses to the very edge of their endurance and beyond, on courses where they can have catastrophic accidents resulting in lethal injury.

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“It’s time we stopped exploiting animals like this for our own amusement. There are plenty of other sports to bet on that don’t involve animals being whipped, breaking their bones or being shot.”

Animal Aid is calling for investigations to be carried out by an independent organisation.