A high quality dog food, preferably a grain free formula would be great for a picky male Cocker Spaniel. My dog is not picky but she has food allergies and I feed her Taste of the Wild. The first 2 - 3 ingredients are meat and there are no fillers, grains, or anything that shouldn't be there. I've heard that the brand I use is great for picky eaters. I hope this helps!
Good suggestion from Pitbull26861. Wysong also makes good quality foods that have worked for my picky eaters. They have recently come out with a new starch free (not just grain free) food called, Epigen.