I think if its mixed with vitamins, those may loose viability, but rest should be fine.
Mine is mixed with salt, so moisture in the air regularly hardens it and sheep still eat it months later w/o issue. Never had mold, a slime, weird smell or anything show up on it.
I’m ashamed to have lost track of it. A bin. In a place. I could put it on my Bermuda hoping the salt would kill it but the grass would probably mutate and do who knows what.