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Comment by rafaelero | Hacker News Reader

This is a very inaccurate picture. Only a minority of cows are grass-fed [1].

[1] https://extension.sdstate.edu/grass-fed-beef-market-share-gr....

Right but that likely means grass finished? Because from what I understand most U.S. beef is grass fed and then finished at feed lots.

Thank you, I actually didn't know this! I'd always heard about the proportion of animals that were raised on grain, as well as the percentage of crops used for animal feed, and concluded that in the US at least the majority of cattle were raised in feedlots their entire lives.

Turns out you're right, the majority start out on pasture and then are transported to feed lots to fatten up once they reach maturity.

According to this[1], due to the fact that grass fed beef fatten up more slowly, end up at a lower overall weight at slaughter, and are kept alive and emitting longer, "a nationwide shift to exclusively grass-fed beef would require increasing the national cattle herd from 77 to 100 million cattle, an increase of 30%", and "the current pastureland grass resource can support only 27% of the current beef supply (27 million cattle)".

Further -

"Emissions of methane, a greenhouse gas with a large warming effect relative to carbon dioxide per molecule, come from beef cattle in the forms enteric fermentation and manure emissions. We calculated a 43% increase in methane from enteric fermentation (table 2), assuming that cattle finishing on grass had the same daily methane emissions as present-day stocker cattle, who have nearly identical ADG and are fed primarily on roughage."

Either way it seems as if grain is an indispensable part of animal agriculture currently, so we have to take that into account when talking about what would happen to land use with or without the cows around. Additionally, it seems that moving away from grain would potentially have even worse impacts on the climate.

[1]https://iopscience.iop.org/article/10.1088/1748-9326/aad401

And your point is? So it's grains or shrooms, or whatever. Something else will grow and die and be broken down into methane its place. Things don't magically stop growing just because the area is no longer used for cattle grazing. Yet it's often magically missing from statistics and calculations when all is said and done...

If you look at the other replies in this thread, there are a number of people pointing out how aerobic decomposition tends to produce primarily CO2, and far less CH4.

"In aerobic composting, the more oxygen that is available, the more carbon dioxide (CO2) produced, the less methane (CH4), and the more complete the decomposition. As biological activity progresses, the oxygen concentration falls and CO2 concentration increases."

https://www.co2meter.com/blogs/news/8056965-co2-in-aerobic-a....

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