Also, crj, you could sprout seeds. The nutritional content of seeds increases enormously from the moment they swell from moisture until they produce the first two green leaves. At that point all the nutrients in the plant's/seed's system go into the production of leaf and stem growth. So, soaking seeds in water, increases their nutrient content daily. I feed soaked seeds regularly. Wheatgrass is enormously nutritious and would satisfy the urge you have to get 'greens' down him. You can buy raw, organic wheat berries at any local health food store. Soak them overnight in a gallon jar of water. Then rinse them in a strainer and keep them in the strainer, rinsing them at least twice a day. Once you feel some of them are ready to feed to him, you can either mash them with a matate, back of a spoon, or even a hammer, or you can (much easier) put them in a blender and osterize them to a liquid state so you can add them to the water he drinks.
Also, with all the amazingly intelligent and well-informed advice and suggestions you are getting in here, I am led to believe that the addition of *enzymes* to his diet would likely be quite beneficial. I have been doing extensive internet research on enzymes and they are having incredible healing results with all kind of afflictions, Autism being one of the most significant.
Sound to me like a possibility that your goose got kicked in the head by a cruel and uncaring member of the human species. That would, indeed, produce all the symptoms you are dealing with. Healing from such an injury does not take just weeks, or even months, but I have seen it take more than a year......even three and a half years for several severe injuries, my own ankle being one of those when I tripped on a stairway. I do not go to doctors so I have rather extensive experience in self-healling. No, it's not because of any religious or philosophical belief system. It is because I grew up in Scottsdale, Arizona, and all my Dad's friends were doctors who gathered in our home in the evenings, and I, as a child, was exposed to their conversations which introduced me to what was going on in their thoughts and minds. I was left with a definite lack of ability or desire to trust the medical profession. So I raised my own kids and backyard animals by doing what you are now with your cherished goose.