According to FAO, livestock is key to food security because food of animal origin provides 1/3 of global protein and essential micronutrients. Environmental sustainability is a challenge for all sectors, including livestock and influences society and the economy. The overall population growth and consequent increase in the demand for food of animal origin has been predicted, especially in developing countries.
Transport, energy production and industry are the largest producers of greenhouse gas emissions. Animal husbandry causes 14.5% of the global release of GHG into the atmosphere of which 40-45% comes from the cultivation of animal feed. Important GHG in livestock are methane, nitrous oxide, and carbon dioxide. Cattle are responsible for about 2/3 of the total, due to methane emissions resulting from rumen fermentation; reducing emission of enteric methane can help mitigate climate change. An important threat to long-term sustainability is ammonia emission from manure along with other reactive nitrogen emissions during feed production. Livestock is estimated to contribute over 40% of global ammonia emissions; these affect smog and small particulate formation, which have toxic effects on human health, surface water eutrophication, and ecosystem acidification.
Although covered GHG emissions, how is possible to quantify livestock environmental impact? A strategic analysis, which considers the animal food producing industries from an environmental point of view, is possible using techniques such as Water and Carbon Footprint as well as Life Cycle Assessment (LCA). LCA is the institutional and international recognized method to assess the environmental impact of a process or a service. This is due to some advantages that it offers: global evaluation of livestock production process (feed production, barn management, purchased material and animals); hot spots individuation and choices to improve management and mitigate impact; comparing different management choices (organic/conventional or small/big farm) or different animal origin food production; supporting decision at farm, regional and national level; identification of environmental burdens and potential effects of interventions. LCA is a tool for quantifying the environmental performance of products taking into account the complete life cycle. It consists of four main phases: defining the goal and scope of the study; making a model of the product life cycle with all the environmental input and output (life cycle inventory – LCI); understanding the environmental relevance of all the input and output (life cycle impact assessment – LCIA); the interpretation of the study.
Feed is the dominant factor determining the environmental impacts of livestock. Improving the efficiency of crops and animals has been a major focus to enable low carbon livestock production. The FAO proposes ways to reduce livestock emissions such as better livestock integration in the circular bio economy. It can be achieved by increasing the share of by-products or waste that humans cannot eat in the livestock feed ration or by recycling and recovering nutrients and energy from animal waste. To fully understand the consequences of this change in feed composition, LCA has been used in animal nutrition to evaluate the environmental impacts of single ingredients and complete diets.
Despite these considerations, LCA and its application to livestock sustainability is a young science. Assessment methods and standards are rapidly developing, but concerns over methodology and appropriate assumptions remain. Variations in system boundaries, assumed inventory data, and functional units make comparisons across studies difficult; although standards and methods give exact numbers, proper interpretation and application remains difficult.