Cows make fog

The title is sort of a joke but contains a truth: I was driving to work admiring the fog hovering over the grass (clear sky above) and noticing it was denser over the marsh and low lying areas. No surprise there. But as I got onto 2A from Lexington Rd,  heading east with a cow field on the right and an open, mowed field on the left, it was surprising to see the fog rising thickly from the cow field and not at all from the mowed field.

It is likely the grass was not the same length or shape from mowing as from mooing (cows) but the difference in fog/no fog was stark enough to require a serious explanation - not a tossed off assumption about physical differences in the grass blade shapes. What to me is far more likely is that bacteria are needed for ground fog and there are lots of them in a cow field and not so much in a mowed field.