The 35-year-old man was unloading sand from a horse-drawn cart at a construction site in Sulawesi earlier this week when the attack occurred,
A witness said the animal suddenly lunged at the man, sinking its teeth into his crotch.
Shocked bystanders loaded the man into a car to take him to hospital, before one noticed a piece of flesh on the pavement.
"Fortunate the horse did not chew up or swallow his testicle, but spit it onto the pavement," the bystander was quoted as saying. "So I picked it up and brought it to the doctor at the hospital where the victim was being treated."
It was not know whether doctors attempted to sew it back on.
The horse had a definite reason for biting this man, could it be that the man was cruel to it and the horse simply sought revenge on him.