They were indeed moldy. I can't figure out how to open the leather one. I soaked them with high-surfactant cleaners, taking care to put the waste water into the garden where the potentially harmful surfactants would be biodegraded quickly.
I have a stack of empty feedsacks. My land is too small to entirely support my two sheep and six ducks through the off-season, so I supplement their grazing with 50 lb sacks of alfalfa and corn. I give most of the empties to a lady at the District Office who makes carry totes from them, but reserved some of them and gessoed their backs.