Not in Fall but certainly in the early winter.I overlooked being out of mineral once when we had an early season snow which melted and turned the grass green.Found three dead and another down out of a group of twenty plus the same day.Fourth one died before the vet had time to get here from the office but he was able to get a blood sample to confirm.
Around here,some of us keep Hi-Mag out the year around figuring it's cheaper to do that than take a chance,some feed hiMag late winter through early summer and some probably still use the old red salt block exclusively.I realize having HiMag out 12 months is like belt and suspenders and probably the middle group have it right