My 13 runners turned 8 weeks old yesterday and I'm buying them some 16% finisher pellets today (looking into Country Lane All Flock). My question is, at what age do you experienced ducks add a ration of oyster shells? Do you wait for them to start laying or just before? I realize this isn't a dire question but I live a while from a feed store so I'd like to make minimal trips. I've been feeding them an 18% starter crumble if that makes a difference. P.S. I have a pair of geese that are a week younger than our ducks. It shouldn't hurt them to move them onto a flock raiser before 8 weeks of age, right?