Myth: Animal agriculture is sustainable.
Sustainability means that cycles are not disturbed and systems are not brought out of balance in the long term.
The consumption of animal products is accompanied by considerable losses of usable biomass. On average, 90% of the energy is lost per trophic level through metabolism and respiration (,). Due to this energy loss, considerably more resources (agricultural land, water, macro- and micronutrients) have to be expended for the consumption of animal products than for the direct consumption of plants. On the one hand, the energy is lost for human use, and on the other hand, it is released into the environment via harmful metabolic products (greenhouse gases, acidifying and eutrophying substances). The high input of resources and the high output of harmful substances disturb the biogeochemical cycles and bring the material flow balances into imbalance.
(1.1) Resource input
One unit of protein from beef production requires 48 times more land than an equivalent unit of protein from pea production. For pork, the ratio is 3:1, for poultry 2:1, for cheese 12:1, for eggs 1.7:1, for fish (farmed) 1:1, and for crustaceans (farmed) 0.6:1. Cow's milk requires more than 13 times as much land as soy milk . This enormously high land use for animal products is manifest-ed in Germany, among other things, by the fact that about 60% of the agricultural land is used for animal feed (, p.32) and yet an additional third of the total protein yield must be imported from overseas for animal feed.
The production of one protein unit of beef requires 6 times more water than the production of an equivalent protein unit from legumes. For pork and lamb, the ratio is 3:1. Chicken protein requires 79% more water than the production of equivalent protein from legumes, protein from eggs uses 53% more water, and protein from milk uses 63% more water (, p. 409).
(1.1.3) Chemical fertilizer
To achieve the high feed yields, chemical fertilizers are applied on a large scale in addition to ma-nure and slaughterhouse waste. In Germany, more than half (56%) of the main fertilizer nitrogen comes from chemical fertilizer (, p.63), which is produced by the particularly energy-intensive Haber-Bosch process.
The high material input in animal agriculture results in increased emissions of metabolic products such as methane, carbon dioxide, nitrous oxide, ammonia, nitrates, nitrogen oxides and phosphates.
(1.2.1) Greenhouse gases
Animal agriculture is a major contributor to climate change, especially due to the high greenhouse gas potentials of methane and nitrous oxide, the clearing of forests, and the opportunity costs of unused carbon sinks. Depending on the calculation method, the share is 18% (, p.271), 28% (, , p.44) and 51% (, p.11). A direct comparison of greenhouse gas emissions from fossil fuels  and greenhouse gas emissions and carbon opportunity costs  from livestock farming illustrates the climate impact of agriculture with livestock.
The production of one unit of protein from beef emits 125 times more greenhouse gas equivalents than the production of an equivalent unit from peas. For pork, the ratio is 19:1, for poultry 14:1, for cheese 28: 1, for eggs 11:1, for fish (farmed) 15:1 and for crustaceans (farmed) 45:1. Cow's milk produces 3 times more greenhouse gas equivalents than soy milk .
(1.2.2) Acidifying gases
Animal husbandry results in high gas emissions of ammonia and nitrogen oxides. By eventually raining off, they enter all ecosystems, causing them to acidify. The acid stress leads to a reduction in plant vitality via an unbalanced supply of nutrients and results in lower plant resistance to drought and frost. In addition, species composition changes. Production of a unit of protein from beef emits 42 times more acidifying gases than production of an equivalent unit from peas. For pork, the ratio is 23:1, for poultry 16:1, for cheese 20:1, for eggs 13:1, for fish (farmed) 8:1 and for crustaceans (farmed) 24:1. Cow's milk produces 8 times more acidifying gases than soy milk . Ammonia is also a gaseous precursor from which harmful secondary particulate matter is formed (, p.107).
(1.2.3) Eutrophying substances
The input of liquid manure and the use of chemical fertilizers result in an oversupply of bound nitrogen and phosphorus in the soil, which cause eutrophication of water bodies, rivers and finally marine areas (North Sea). In large parts of Germany, the inputs permanently exceed the pollution limits (, p.76). Eutrophication favors nutrient-loving plants, displaces nutrient-sensitive plants and thus leads to a loss of biodiversity among plants, insects and animals. In lakes and oceans, entire ecosystems are collapsing. The production of one unit of protein from beef causes 44 times higher loads of eutrophic substances than the production of an equivalent unit from peas. For pork the ratio is 14:1, for poultry meat 8:1, for cheese 13:1, for eggs 6:1, for fish (farmed) 30:1 and for crustaceans (farmed) 45:1. Cow's milk results in 10 times more euthrophic substances released to surface water than soy milk .
(2) Use of herbicides, fungicides and insecticides.
The high demand for feed for livestock requires intensification of agriculture using herbicides, fungicides and insecticides. In Germany, such agents with more than 32 thousand tons of active ingredient (, p.54) were sold in 2016. On the one hand, herbicides, fungicides and insecticides are harmful to human health via water and food intake. On the other hand, they significantly damage insect populations. At representative sites in Germany, an average decline in insect biomass of 76% has been measured over 27 years . The decline in insects in turn has an impact on plants and animals. For example, about 80% of wild plants depend on insects for pollination , while 60% of birds depend on insects as a food source .
Overall, the use of artificial fertilizers and herbicides, fungicides and insecticides, the loss of insects, the high demand for land and thus the displacement of plants and wildlife, and the high emissions of acidifying and eutrophying substances are reasons for the loss of biodiversity leading to a decline in plant diversity and animal populations  and the observable sixth mass extinction of species. The extinction rate is 117 times higher than would be expected without human impact . Most endangered species are native to South America, Asia, and Oceania, but livestock production in Germany also bears a causal share of responsibility for the extinction events there due to high feed imports and the associated clearing of rainforests.
(3) Use of antibiotics
Animal husbandry requires a high use of antibiotics. They are used to a small extent against individual animal diseases, but for the most part prophylactically and to accelerate the growth of the animals and thus their readiness for slaughter. In 2019, 670 tons of antibiotics were used in veterinary medicine in Germany, including 131 tons of reserve antibiotics classified by the WHO as “High-est Priority Critically Important Antimicrobials for Human Medicine” . By comparison, 666 tons of antibiotics were consumed in human medicine in Germany in 2016 (, p.6).
The use of antibiotics, especially in animal agriculture, leads to dangerous antibiotic resistance, which impairs the effective treatment of infectious diseases in humans and animals. In Germany about 6000 people die of multi-resistant germs every year. The WHO classifies antibiotic resistance as one of the greatest threats to global health, food security and development .
(4) Cause and driver of zoonoses and pandemics
Livestock farming, with its high density of animals and its high land requirements, is one of the main reasons for diseases that can be transmitted from animals to humans (zoonoses) and ultimately for pandemics. High animal husbandry densities promote the development of pathogens within animal husbandry and the likelihood of their spreading to humans. The enormous amount of space required by animal husbandry for feed and pasture displaces wild animals from their habitats and brings them into contact with domesticated animals and humans (, p.15-19). More than 70% of all new diseases occurring in humans are zoonoses (, p.5). Almost 100% of pandemics are caused by zoonoses (, p.8).
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services IPBES has therefore identified meat consumption and animal husbandry, among other things, as pandemic high-risk activities and proposes appropriate taxes and levies.In addition, the Council calls for the economic costs of pandemics to be factored into consumption and production and for funds to be made available for transformation processes in government budgets (, p.8 ).