"As valuable as animal protein is, livestock are relatively inefficient protein-making machines. ...only 23 percent of the protein that a cow takes in ends up as usable protein in its meat or milk. Beef cattle pay back about 10 percent... while pigs return 12 percent. ...Grazing in a pasture, a 1,000-pound cow turns the grass into edible protein at the rate of about a pound a day. The same weight of bacterial organisms... produces 2,750 pounds of protein in the same "grazing" day. Bacteria are also less demanding... they do not care what the weather is and do not need as much personal attention..."