Khaki Campbells hatched May 20th. Purchased at feed store as day olds. One out of 5 purchased hasn't been growing well the last week to 10 days. Falling behind the others. This morning it's neck is twisted, it can't walk normally and can barely stand. It is still eating and drinking a small amount if I hold the food in a position it can reach. Has been feed only nonmedicated game bird starter 26% protein purchased at Agway feed store. Any ideas what is wrong and how to take care of this duckling?