Hi Offwego and Rhys,
I’ve thought about the same issue myself when my friend received a (tractor)bucket load of horse muck to the tune of 1 ton. It strikes me that no dig follows nature relatively closely as a principle. Now, in the great scheme of things, horses do not produce 1 ton of manure at any 1 time!
I feel that the rotting process inside could be anaerobic, producing the bacteria we do not want. The science seems to support Rhys’s approach of mixing woody and wet composting material helping oxygenation.