A large percentage of muck we remove from farms is hauled to Anaerobic Digestion plants. Anaerobic Digestion is a renewable energy source, and is a natural process where plant and animal materials are broken down by micro-organisms in an air-tight tank/digester. This releases a biogas that can be used to generate heat, power or transport fuel (Source: http://www.farmrenewables.co.uk/how-ad-works.html).
Muck can also be spread on the land, and with poultry muck containing decent amounts of Nitrogen, Phosphate, Potash, Magnesium and Sulphur it can be used as a natural equivalent to fertiliser. For this, we would tip the muck at a location of choice for the farmer to then distribute.