I call bull on these numbers.
Figure that a side of beef weighs what? 500 lbs? Times 2 for 1000 lbs total. That's 4000 quarter pounders, if you were to grind it all up. (which I wouldn't. I like filet. :-) )
Means that the cow eats over 12 tons of grain. And took up over 6 acres of grazing land, on top of that.
Even halving the numbers would be ridiculous.
30 lbs a day of forage seems to be the number
not sure how many days to slaughter
http://www.thebeefsite.com/articles/3154/how-much-forage-does-a-beef-cow-consume-each-day