Reducing the Environmental Impact of Animal Production

Abstract

Global food demand will increase in the next 30 years to meet the needs of the increasing population. Demand for animal products (meat, milk and eggs) is likely to increase at a faster rate than the demand for cereals. There is pressure to reduce the environmental impacts of livestock systems, particularly greenhouse gas emissions (GHG) and excretion of nitrogen and phosphorus. The main driver of environmental impact in animal systems is production efficiency, i.e. output of milk, meat, eggs or pollutants per unit of input. Production efficiency is related to performance per animal, reproductive rate and replacement rate. Higher production efficiency means that fewer animals are needed per unit of the product so that ‘unproductive’ emissions and excretions associated with maintenance and the rearing phase are spread over more units of product. Nutrition can reduce emissions and excretions per animal. Methane emissions by ruminants are related to the quantity of forage digested, so increasing dietary proportions of concentrates, and increasing starch or fat content at the expense of fibre will reduce methane per unit of product. Genetic selection for low methane emissions should only be considered alongside feed efficiency. Nitrogen and phosphorus excretions are related to dietary nitrogen and phosphorus contents, particularly with excess supplies. Precise diet formulation, using rumen degradable and undegradable protein requirements in ruminants, and digestible amino acid requirements in non-ruminants, can reduce nitrogen excretion. Reducing phosphorus content of diets, and phytase enzymes in non-ruminant diets can reduce phosphorus excretion. In conclusion, the main strategy for reducing the environmental footprint of livestock systems must be to reduce wastage of breeding animals through premature culling for fertility and diseases. This will also improve profitability. Therefore, a whole-system approach is needed which considers the environmental cost of diet formulation as well as economic cost.