Prehistoric humans may have practiced brain surgery on cows.

Prehistoric surgeons may have practiced dangerous skull opening procedures in cows before operating on people.
A previously excavated cow skull from a settlement of approximately 5,400 to 5,000 years in France contains a surgically created hole in the right side, a new study finds. There are no signs of bone healing, which begin several days after an injury, around the opening. One or more people may have tried surgical techniques on a dead cow or unsuccessfully tried to save the life of a sick cow in what would be the oldest known case of veterinary surgery, the researchers conclude online on April 19 in Scientific Reports .
Evidence of skull surgery in humans, whether for medical or ritual reasons, dates back to about 11,000 years ago (SN: 5/28/16, p.12). The ancient surgeons needed to know how and where to scrape the bone without damaging brain tissue and blood vessels. Therefore, it is plausible to practice bone extraction in cows or other animals.
The opening of the cranium of the cow, almost in square shape and framed by scraping marks, resembles two cases of human skull surgery of the same period in France, say biological anthropologists Fernando Ramírez Rozzi of the CNRS in Montrouge, France, and Alain Froment of the IRD -Museum of man in Paris. The microscopic and X-ray analyzes found no fractures or splintered bones that would have been goring from the horn of another cow. Nor did any typical damage appear from someone hitting the head of the cow with a stick or other weapon.