Displacement ratios for US corn DDGS
With large-scale biofuel production, co-products such as dried distillers grains with solubles (DDGS) are increasingly being used in animal feed rations. In the process they displace various other inputs, reducing the need to produce them. This results in avoided GHG emissions, also known as GHG credits. GHG credits of biofuel co-products are routinely used in life cycle analysis of biofuels and are calculated using the displacement ratios of co-products. Indirect land use change (ILUC) models also implicitly capture the GHG credits of co-products by modeling substitutions among co-products and animal feed ingredients.
The displacement ratios used in existing US studies are less precise because they are derived from field-based animal experiments that rely on simple diets in the Midwest US. In reality, animal diets vary across regions depending on the price and availability of feed ingredients. Moreover, the animal feed industry uses least cost optimization software to formulate animal diets such that nutritionally balanced diets are obtained at the least cost.
To improve our understanding of corn DDGS use and provide better estimates of the displacement ratios of corn DDGS, a new study commissioned by the ICCT looks into regional variability of diets for ruminants, swine, and poultry informed by the price and availability of feed ingredients. Using least cost formulation software, this study estimates DDGS displacement ratios by regions and by livestock types. The study provides aggregate displacement ratios of corn DDGS for use in life cycle analysis and informed ILUC modeling. The key findings of the study are:
- Regional variations in animal diets are more pronounced for ruminants than for non-ruminants and this variation is reflected in the DDGS displacement ratios. Adding 30% DDGS in beef diets displaces about 24% of corn in the high plain where simpler diets are found, whereas it displaces about 2% of corn in the West, where diets are more complex.
- Corn DDGS displaces a wide range of animal feed ingredients rather than only a few ingredients such as corn and soybean meal as suggested by earlier studies. In aggregate, 1 unit of DDGS displaces 0.554 units of corn and 0.072 units of soybean meal in the US, which combined together account for 63% displacement on a mass basis. Besides, 21 other feed ingredients are displaced, accounting for 51% displacement.
- The use of DDGS increases the use of corn silage, wheat straw, vitamins, and amino acids and other ingredients, contributing a negative displacement of 14%. In total, 1 unit of corn DDGS displaces 1 unit of animal feed on a mass basis if the baseline animal feed is nutritionally optimal.