While deer can be killed with shotgun, it is an inferior choice, IMHO, to be used only if required. Here's why: buckshot is a close range <40 yard proposition, and... slugs hurt to shoot, and sabot slugs are expensive.

I've killed deer with shotgun; I occassionally carry with buckshot early in season, if doing a drive, or later if running dogs and required... but it isn't my first choice.