Livestock production--primarily cows--produce 14.5 percent of global greenhouse gas emissions. The majority of that is in the form of methane, a potent greenhouse gas that is a natural byproduct of how some livestock process food. But as Christopher Booker reports, scientists are hoping that small tweaks in what cows eat can dramatically reduce a big source of climate emissions. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders