Egg yolks and whole eggs are a good source of protein and choline. For this reason, the United States Department of Agriculture (USDA) categorises eggs as Meat. Chicken eggs that are produced commercially for eating have not been fertilised by a rooster and, therefore, cannot develop into embryo and finally a chick. It is possible to enrich table eggs with minerals (e.g. iron and iodine), antioxidants (e.g. selenium, vitamin E) or omega-3 fatty acids and vitamins, by adding these as components of the hen diet. There are some enriched eggs available in Australia but this represents a niche market for eggs, as only a small percentage of consumers purchase such eggs.