Livestock farming systems produce milk and meat for human consumption. The milk and meat provide important nutritional compounds, especially protein. Nomadic derive their nutrition almost completely from milk and meat from ruminant animals, but for most people, animal protein supplements a predominantly vegetable diet with essential amino acids and vitamins that are in short supply in vegetarian diets. Consumption of animal proteins is related to human culture but also to the level of prosperity; the higher the standard of living the larger the consumption of animal protein. The increase in human population, together with the increase in the standard of living in developed countries, are the main reasons for the rapid growth in numbers of farm animals worldwide and also for the increased impacts of livestock farming systems on the biosphere during the last few decades.

Raising livestock for human consumption generates nearly 15% of total global greenhouse gas emissions, which is greater than all the transportation emissions combined. It also uses nearly 70% of agricultural land, contributing to deforestation, biodiversity loss and water pollution.