Botulism: It Takes Less to Kill a Horse than a Mouse! Register now for Ask TheHorse Live “Botulism: Deadly to Horses” Thursday, Aug. 9, 8 p.m. EST! For more information click the link below! Botulism in horses Fact: It takes less botulism toxin to kill a horse than a mouse. Yet, it might lurk in your horse’s hay. Find out why horses are at risk and how to protect them.