See my post 27
Coprophagy, or feeding on manure, is not new in animal nutrition. For example, livestock feeding on a farm has frequently involved a system of beef cattle followed by hogs and subsequently chickens. Under such a programme the nutrition of the hogs and chickens is based on manure. The current interest in manure as a feedstuff is mostly due to the problem of waste disposal from intensive livestock and poultry operations. Apart from this problem it has been recognized that large amounts of nutrients are wasted. The re-use of manure is one way of creating edible protein from waste material which is often disposed of uneconomically and also creates a nuisance. The amount of excreta produced is considerable: a 2-kg hen produces 0.8 kg a week, a 650-kg cow 150 kg, an 80 kg pig 40 kg and a 45 kg pig 22 kg.