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.