FILE - This June 18, 2009 file photo shows cows grazing in Rock County, Neb. Compared to the other animal proteins, beef produces five times more heat-trapping gases connected to global warming per calorie, puts out six times as much nitrogen for water pollution, takes 11 times more water for irrigation and uses 28 times the land, according to the study published Monday in the journal Proceedings of the National Academy of Sciences. (AP Photo/Bill Wolf, File)
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