How many glasses can a cow produce in its lifetime?

Not sure, but . . .I can tell you with a high degree of certainty how much a cow produces in a year.

Although the amounts vary from cow to cow depending upon many variables, including the quality of the feed given to the animals, a dairy cow cranks out about 142 kilograms of methane per year. (The U.S. EPA says it's more like 100 kg/yr.) Beef cattle don't fart as prolifically, squeezing out only about a little more than half as much methane, 76 kg/yr.

Note that those figures DO NOT take into consideration the amount of methane produced by the decomposition of manure.

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Just to be clear, cattle and other ruminants release methane primarily by belching. It is a common misconception that cows are monstrously flatulent.