It turns out that it isn't cow flop that’s causing the problem, but rather, it's cow belches.
That's according to a study that found less than half the air pollution attributable to cows comes from their excretions. About sixty percent comes from “cow burps”.
I'm not surprised, seeing as cows have stomachs with four compartments, compared to the single-compartment stomach in humans.
The reason is the food they eat (it’s not just grass). It’s hard to chew, and tough to digest. Cows swallow food without chewing much. They store their unchewed meals in their first two stomachs: the rumen and the reticulum.
Later, while at rest, cows belch up parts of their unchewed meals, which is called “cud” (hence the term “chewing their cud”). This time around the cows chew the food well, swallow it, and send it to their third and fourth stomachs: the omasum and abomasum.
That’s where it’s digested. Some of it becomes milk. The rest becomes air pollution.