A method of treating waste matter from animals, the method comprising: a) collecting waste matter from the animals； b) inhibiting urease activity in said collected waste matter； and c) separating said urease-activity inhibited waste matter into a urea-rich fraction and a urea-lean fraction； a system for treating waste matter from animals； a urea-lean biogas fuel product； a urea-rich animal waste-matter product； a method of controlling the content of nitrogen in manure from animals； a method of reducing gaseous ammonia in stables for animals； a stable for animals； a biogas reactor system for producing biogas from waste matter from animals； a method of producing urea from waste matter of animals； a method of producing urea formaldehyde； and a method of producing biogas fuel from waste matter of animals.
