How many more horses killed?
https://www.horsedeathwatch.com/
The numbers are astoundingly high.
I grew up on a horse breeding and racing stable. In 20 years we didn't have a single horse die on a racecourse.
We had one have a heart attack while training (autopsy revealed she had a malformed heart).
Other horses died in accidents (very rarely, usually from attacking another horse). Colic, triggering them to roll and getting a twisted bowel was a scary and likely risk.
Most deaths were in labour, despite hours of struggling over them and huge vets bills.