As that Zootechnie article implied, I believe that most of the methane produced by a cow or other ruminant comes to the surface, so to speak, when the animal 'burps' up a cud for re-chewing. If you have ever been close enough to its mouth to smell the gas when it happened, you'll know what I mean.

Some of you may have heard/read of the phenomenon of lighting the gas from a stuck distended stomach ('stuck' as in pierced). It's very real. Sometimes when veterinarians performed the minor surgery they went the extra step for the benefit of awestricken children.

Ebbie