A just-published analysis of data received from a satellite in 2004 has shown that at least during that year, livestock in the U.S. emitted more methane into the atmosphere than did the oil and gas industry. In their article published in Journal of Geophysical Research: Atmospheres, a team of researchers from Harvard University, California Institute of Technology and the University of California studying the data note that such emissions were far higher than was reported by the U.S. Environmental Protection Agency (EPA).
Specifically, the researchers found satellite data showed livestock emitted 13 million tons of methane over the summer in 2004 (the EPA reported 9.7 million tons). They found the satellite data also showed that the combined emissions of the oil and gas industry amounted to 7 million tons (the EPA reported 9.9 million tons).
Unfortunately the sensor on the satellite was unable to show methane amounts after 2004, thus more data is not available. That will, however, change soon as a new satellite with sophisticated atmospheric gas monitoring sensors aboard is set to launch next year. More information on the role that methane plays in changing our climate can be found here.
Yes, if bison herds were the same size as commercial cattle herds are now then they would have the same problem. But they are not, were not and will not ever be that size.
Huh? Bison ranged across the plains in herds estimated from a total of 50 million on up. I doubt very much you have anything close to the same number of cattle currently in the same area. You couldn't, cattle are very hard on arid range. The numbers of bison have increased from a few dozen animals in the early 20th century when they were nearly wiped out to roughly 500,000 today, with strictly limited range available to them. Eliminate the cattle and the fences, set them free to roam (look up Buffalo Commons) and their population will increase rapidly. Since they are generally more beneficial to the land than cattle, more of them can survive in the same area.