The purpose of "wolf collars"

"A sheep showing gratitude to the dog that saved him from a wolf attack.  Notice the spike collar (not dog’s blood)."

You learn something every day.  I had seen photos of spiked collars on dogs and assumed they were just decorative or fanciful; I didn't know they derive from a European tradition of having dogs protect livestock from wolves.

A wolf collar (also known as Italian: roccale or vreccale, Spanish: carlancas) is a type of dog collar designed to protect livestock guardian dogs from attack by wolves. Wolf collars are fitted with elongated spikes to stop wolves from attacking dogs on the neck. Such collars are used by shepherds in many countries including Italy, Spain and Turkey.  [photos at the link]