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Here's some help with the facts.

160 million acers of public land are leased to ranchers at below fair market value.
http://www.blm.gov/wo/st/en/prog/grazing.html


http://people.oregonstate.edu/~muirp/wpubland.htm
What percentage of US beef production relies, at least in part on these western public rangelends? Well, this question is very difficult to answer, in part because many western livestock owners use not only public but also private grazing lands, and because cattle spend various proportions of their feeding lives on the public lands. Suffice it to say, however, that the percentage is probably quite small (significantly less than 10%; probably between 2% and 4%).