Many people ask what to feed their new goslings (or ducklings). Here is what I do and why.
I use a grower food with 20% protein (Like Purina flockraiser), and mix it 3 parts grower, 1 part rolled oats and 4 pinches (about a tsp each) of brewer's yeast. The grower is a pre-mixed food for growing birds. The rolled oats are to reduce the protein level to avoid angel wing. Angel wing is a common disorder in water fowl. You can read more about it here; http://www.metzerfarms.com/AngelWing.cfm?CustID=81775
I add the brewers yeast for vitamins and niacin that waterfowl babies need for healthy legs.
When the birds are 1 week and older, I start to mix a couple of handfuls of organic scratch n peck (http://www.scratchandpeck.com/) brand layer food into the above mix. This is a high quality food and is important for good feather development.
When geese are grown, you can feed them a layer crumble with 16% protein. I prefer to feed a little higher protein when they are molting and growing new feathers.
**Remember that geese, especially developing goslings are supposed to have 1/2 to 3/4 of their diet in grass! If you keep them penned up then you will have to pick it for them daily.
Please do your research on feeding what is right for your birds so that you can raise the most healthy birds you can.