Averaged over 20 years, methane traps around 72 times more heat than CO2. Over a 5-year period, methane is seen to be even more potent, trapping around 100 times more heat than CO2. At the same time, methane leaves the atmosphere within a decade, while CO2 will stay around warming the planet for hundreds, possibly thousands of years.
The UN points out that livestock is the single greatest source of methane, at 36 percent of total anthropogenic methane. Furthermore, because methane is a building block of ozone, reductions of methane anywhere will reduce ozone, which is the third most prevalent greenhouse gas after CO2 and methane.