Nutritional and greenhouse gas impacts of removing animals from US agriculture

Abstract

As a major contributor to agricultural greenhouse gas (GHG) emissions, it has been suggested that reducing animal agriculture or consumption of animal-derived foods may reduce GHGs and enhance food security. Because the total removal of animals provides the extreme boundary to potential mitigation options and requires the fewest assumptions to model, the yearly nutritional and GHG impacts of eliminating animals from US agriculture were quantified. Animal-derived foods currently provide energy (24% of total), protein (48%), essential fatty acids (23-100%), and essential amino acids (34-67%) available for human consumption in the United States. The US livestock industry employs 1.6 × 10⁶ people and accounts for $31.8 billion in exports. Livestock recycle more than 43.2 × 10⁹ kg of human-inedible food and fiber processing byproducts, converting them into human-edible food, pet food, industrial products, and 4 × 10⁹ kg of N fertilizer. Although modeled plants-only agriculture produced 23% more food, it met fewer of the US population's requirements for essential nutrients. When nutritional adequacy was evaluated by using least-cost diets produced from foods available, more nutrient deficiencies, a greater excess of energy, and a need to consume a greater amount of food solids were encountered in plants-only diets. In the simulated system with no animals, estimated agricultural GHG decreased (28%), but did not fully counterbalance the animal contribution of GHG (49% in this model). This assessment suggests that removing animals from US agriculture would reduce agricultural GHG emissions, but would also create a food supply incapable of supporting the US population's nutritional requirements.

Keywords: agriculture; food; food security; greenhouse gases; livestock.

Fig. 1.

United States food production as an ecosystem with transactions between components as identified in this study. Crops are processed or consumed directly by animals. Processing products and byproducts are shuttled to industrial applications or to animals and humans for consumption. Animals provide manure used to produce crops, byproducts used in a variety of industrial applications, and human food. Values are those calculated for the present study. Adapted with permission from ref. , copyright (1997) American Chemical Society.

Fig. 2.

Total HRYs produced in 2013-based US food production systems with actual animal-derived food inputs or modeled without animal-derived food inputs (plants-only). The gray vertical rectangle indicates the number of HRYs needed to meet requirements of the US population. Grayed boxes indicate HRY production inadequate to meet US population requirements. Energy and protein HRYs required for pets were subtracted from the plants-only diet.

Fig. 3.

Amounts and proportions of foods available in systems with and without animal inputs. Graphs are sized proportionally to the amounts of food available.

Fig. 4.

Comparison of the daily diet composition, CO₂e emissions, intake, cost, and nutrient adequacy of the current US diet compared with a series of optimized diets with and without (modeled) animal-derived foods. Bar graphs indicate dietary adequacy of specific nutrients by scenario; purple indicates current diet, blue indicates diet with animals, yellow indicates plants-only diet. “Other” represents nuts, legumes, fats, and sweeteners. ArachA, arachidonic acid.

Fig. 5.

GHG emissions associated with food production in a system representative of the current United States and a modeled system in which animal-derived food inputs are eliminated.