I stumbled across this question and answer while surfing today and it does the best job of addressing the Vegan question I could find.
The original of this is available at: http://www.ansi.okstate.edu/breeds/
“Why do we have livestock at all? Don’t they just eat the food that would be better utilized by being given directly to people?”
“Food is, by far, the most important contribution of agricultural animal, although they rank well behind plants in total quantity of food supplied. Plants supply over 80 percent of the total calories consumed in the world. Animals are a more important source of protein than they are of calories, supplying one-third of the protein consumed in the world. Meat, milk and fish are about equal sources of animal protein, supplying, respectively, 35%, 34% and 27% of the world supply of total protein.
There are many who feel that because the world population is growing at a faster rate than is the food supply, we are becoming less and less able to afford animal foods because feeding plant products to animals is an inefficient use of potential human food. It is true that it is more efficient for humans to eat plant products directly rather than to allow animals to convert them to human food. At best, animals only produce one pound or less of human food for each three pounds of plants eaten. However, this inefficiency only applies to those plants and plant products that the human can utilize. The fact is that over two-thirds of the feed fed to animals consists of substances that are either undesirable or completely unsuited for human food. Thus, by their ability to convert inedible plant materials to human food, animals not only do not compete with the human rather they aid greatly in improving both the quantity and the quality of the diets of human societies.”
[There is a table in the original doc that this refers to. Ommited here. See the original source if necessary]
“Only about one-third of the land area of the world is classified as agricultural. Thus, roughly two-thirds of the land area of the world is not suited for any sort of agricultural use because it is covered by cites, mountains, deserts, swamps, snow, etc. Of the 35 percent that can be devoted to agriculture, less than one-third (or about 10% of the total land area) can be cultivated and produce plant products that the human can digest. The remaining two-thirds of the world’s agricultural land is covered by grass, shrubs or other plants that only ruminant animals can digest. Thus, the inefficiency of animals is not a major concern since they represent the only way these plants can be converted to human food. As the human population of the world increases, it is likely that we will be forced to depend more and more on ruminant animals to meet the increased demands for food.”
