milk, baby formula has an expiration date beyond which it is unfit for human consumption. Manufacturers, who must discard millions of pounds of outdated formula annually
Of course it can be done, IF match with local sanitary regulations. Usually those kind of food to be recycled need a heat and pressure treatment, also asses it's chemical composition to be included into an specific animal diet.
Yes, however you need to consider the animal in question. Human milk is rather unusual in its high lactose content and low fat and protein contents. So check and try to match the ideal composition by supplementing as necessary.
Yes, harnessing that as an ingredient in formulation of animal fed is possible. You only have to follow the principles of feed formulation including purpose, nutrient requirement of animal, inclusion rates, among others. Very importantly you need to ensure the quality and safety of the that ingredient before its use.