Role of ruminant livestock in sustainable agricultural systems.

Ruminants have served and will continue to serve a valuable role in sustainable agricultural systems. They are particularly useful in converting vast renewable resources from rangeland, pasture, and crop residues or other by-products into food edible for humans. With ruminants, land that is too poor or too erodable to cultivate becomes productive. Also, nutrients in by-products are utilized and do not become a waste-disposal problem. The need to maintain ruminants to utilize these humanly inedible foodstuffs and convert them into high-quality foods for human consumption has been a characteristic of advanced societies for several thousand years. Further, ruminant livestock production is entirely consistent with proper agronomy practices in which forages are grown on 25% of arable land to minimize water and soil erosion. Questions have been asked, however, about the use of humanly edible foodstuffs (grains, protein sources, etc.) in ruminant diets. Does their use create a net loss of nutrients for human consumption? What level of their use is necessary or desirable? Does the use of some of these improve the nutrient (e.g. protein) quality or product value? Too often the opponents of animal agriculture evaluate the desirability of animal production on gross calorie or protein intake/output values. However, in many cases the feeds used in animal production are not consumable by humans, and in order to properly evaluate animal production, humanly consumable energy and protein intake should be used for efficiency comparisons. Analysis of the costs/returns of humanly edible energy and protein for a variety of dairy and beef cattle production systems shows that food value is increased with ruminant products, and that net returns of humanly edible nutrients are dependent on the production system used. The efficiency with which ruminants convert humanly edible energy and protein into meat or milk is highly dependent on diet, and hence, on regional production practices. Previous studies suggest that in the United States, dairy production efficiency ranges from 96 to 276% on a humanly consumable protein basis. Beef production efficiency is very dependent on the time spent in the feedlot and digestible energy and protein efficiencies range from 28 to 59% and 52 to 104%, respectively. However, beef production can add to the humanly consumable protein pool depending on the feeding schedule. In addition, the protein resulting from ruminant livestock production is of higher quality with a greater biological value than protein in the substrate feeds. The evidence that ruminant livestock belong in sustainable livestock production systems is convincing.