[bert]

I think that manure = Ammonia

[Bryanw92]

It is H2S and Ammonia. But Ammonia will still assault your senses while it is at a deadly level.

[pfflier]

All kinds of mechanisms at work. Ammonia and hydrogen sulfide are downright poisonous. Combine them with methane and carbon dioxide and you displace breathable air even if the other gasses don’t reach lethal levels.