The rumen is like a huge bathtub, he said, holding about 50 large soda bottles’ worth of fluid redolent with bacteria. Relying on these symbiotic microbes, cows eat up to 150 pounds of grass a day, a food inedible to most animals, including humans. Hess was after those microbial secrets, and the placid heifer was happy to oblige.
“You can just do your experiment,” he said later. “The cows don’t really care.”
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