I have a dozen ducklings, and not all related. They are all having trouble walking. They have been growing fast and eating and drinking fine. However, I found two dead today. The next one I may take to MSU. They are on a sand floor, so I put alfalfa on top in case they are ingesting too much sand. The sand is the only thing I have done different this year. They are with a dozen chicks, and the chicks are just fine. All share a 25 square foot brooder, and have plenty of clean water and non-medicated chick starter. All are almost 2 weeks old. Any ideas?