Why do veterinarians wear a white jacket and a tie?

Business casual plus a white lab coat is something of a uniform for some veterinary practices - it was adopted from the human physician community. However, not all veterinarians wear this - some work in surgical scrubs all day, others wear jeans and a polo shirt, others wear khakis and a polo shirt, etc.

I work as a public health veterinarian, and I wear jeans and a T-shirt to work then change into a set of white pants and a white button-down shirt once I get there.