Nutritional and greenhouse gas impacts of removing animals from U.S. agriculture

Authors: WHITE, ROBIN - Virginia Polytechnic Institution & State University; Hall, Mary Beth

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2017
Publication Date: 11/13/2017
Citation: White, R.R., Hall, M. 2017. Nutritional and greenhouse gas impacts of removing animals from US agriculture. Proceedings of the National Academy of Sciences. 114(48):E10301-E10308. doi: 10.1073/pnas.1707322114.
DOI: https://doi.org/10.1073/pnas.1707322114

Interpretive Summary: Reports on the impact of animal agriculture on the environment, use of resources, and the human diet have raised the question as to whether animal agriculture should be reduced or eliminated. That question needs to be evaluated in the context of the integrated ecological system in which human society exists with plant and animal agriculture. We modeled the United States agricultural system with or without the inclusion of animals to evaluate the impact on adequacy of the food supply without supplements to meet the nutrient requirements of the U.S. population, and on greenhouse gas production. Without animals in the system, lands cropped for animal agriculture were converted to human food production with acreage increases for each crop proportional to what the food crops account for in our current system. Untillable pasture and range were not used. When animals were omitted, diets formulated based on available foods were deficient in more nutrients, notably calcium, vitamin A, vitamin B12, and specific fatty acids. Based on available foods and the combination that would meet nutrient requirements, grains accounted for more than 80% of the diet, as the resources of vegetables and fruit from currently imported or U.S.-raised sources were not adequate in composition or amount to meet needs. Greenhouse gases increased slightly without animals because the manure they produce would have to be replaced by synthesized fertilizer. Removal of animals from the U.S. agricultural system would not meet the nutritional needs of the U.S. population and would not reduce the environmental impact of greenhouse gases.

Technical Abstract: Livestock’s Long Shadow designated the livestock sector as one of the most significant contributors to environmental problems. Offered solutions for this situation have ranged from modifications to, downsizing, or elimination of animal agriculture. A challenge in assessing any of the options are the number, accuracy, and complexity of assumptions that must be made regarding viable approaches and impacts. The scenario that requires the fewest assumptions is the elimination of animal agriculture, which also provides the boundary to the potential impact of other intermediate measures. The yearly nutritional, environmental, economic, and social impacts of removing animals from U.S. agriculture were quantified. Animal-derived foods currently provide 32% of the energy, 61% of the protein, and more than 36% and 55% of essential fatty and amino acids available to meet nutrient needs of the more than 316 million people in the U.S. The U.S. livestock industry employs 1.4 million people and accounts for $31.8 billion in export goods. Livestock recycle 72.8 billion kg of human-inedible food and fiber processing byproducts, converting them into human-edible food, industrial products, and 34 billion kg of N fertilizer each year. In addition to food and fertilizer, byproducts of livestock production contribute 4.2 billion kg rendered protein and 4.6 billion kg fat which are used for manufacturing and pet food. Although domestic plant-based production was sufficient to meet most nutrient demands, eliminating animal production made it infeasible to meet the U.S. population’s requirements for some nutrients that are in low concentrations in plants. When adequacy of the nutrient supply was evaluated on the basis of least-cost diets produced from foods available, more nutrient deficiencies and a greater excess of energy were encountered in plant-only diets. Potential food energy and protein exports were greater with plants only, but food lysine exports depended upon exclusion or use of imported foods. In a modeled system with no animals, estimated agricultural greenhouse gas emissions (GHG) nominally increased (2.5%) primarily due to counterbalancing impacts of synthesizing fertilizer to replace manure. A whole-system assessment of U.S. food production suggests that a plants-only agricultural system is not adequate to meet the nutritional needs of the U.S. population and will not reduce environmental impact of GHG.