I think the whole difference is that in modern times horse breeders and owners use wood shavings for bedding. This matter is anything like that old manure with straw used for hot beds. In fact I do not think it could heat up like that old stuff. The manure lacks moisture. I was using stuff from my neighbour's pile which was at least five years old if not more, on my perennial flower bed that I reworked last your ( by the way I dug up hundreds of daffodils in the process and none were rotted. No evidence of Narcissus fly). It was more like bagged wood chip mulch. I can see that this stuff could grow mycelium under the right circumstances. Bea zone 5