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These recollections are from a decade or more back. It may well be than the effeciency in meat production is much improved. I will be a bit suprised if this is not so. As ugly as industrial animal processing may appear, my guess is that it must be more effecient at producing table meat that more traditional methods...
In the book super freakonomics, they examine another food based study which supported this. They found that large super farms are more efficient at feed to meat conversion. They also determined that the majority of CO2 emissions in the food supply chain come from production not transportation. Transportation accounts for around 8% of these emissions. They concluded, based on co2 emissions, large super farms that ship long distances produced less co2 waste than smaller local farms that transported shorter distances. This didn't take into account the quality of meat, animal treatment or methane production. With regards to CO2 and feed conversion, you're right. Large industrialized farms are more efficient.