He needs a complete feed like you buy at a feed store or TSC, Is he actually eating all the above? I have never been able to get my ducks to eat yogurt-apple- or egg yolk. I do use whole oats in their feed. He needs some extra nutrients to help him heal. Do you think he is a crested duck and someone[ducks] pulled all the feathers out? Poor thing is it drake or duck? as for it's wounds, I'd clip the feather some around the chest wound and clean real good with betadine or Epsom salt water then put Neo sporin on both places. and your really going to have to watch for flies because they will lay eggs in the wounds and wreck havoc they can even kill this duck. I commend you on trying to help and hopefully with a little more work and TLC you'll get it healed up. I would keep the duck inside away from flies till wounds are closed up. There is also a product called Veterycin spray from wounds and infections that is great for something like this. Please keep us updated on his