Possibly fed, possibly just tame, or the other possibility is salt. Those of us not the fairer sex have
a habit of "watering trees" instead of finding a privy, and I know I've had deer very interested in licking urine. Yeah it's nasty but kinda natural. Here in alberta where there's lots of oil exploration, they cap old well sites all over and often there's lots of dredge up and oil mud near where the well head was that is high salt content that deer will also hang around and dig/lick up. Makes the right old well sites handy places to hang around on the downwind side if you like venison }8->