The life cycle assessment (LCA) is a widely used tool to assess the potential environmental impacts of livestock supply chains and of resultant products.A central question in such approaches is how environmental burden and benefits are distributed among livestock products and how to consider manure that is widely used as production input in agriculture for nutrients besides being also a biofuel source.

The research article The value of manure - Manure as co-product in life cycle assessment (Leip et al., 2019), published by the technical advisory group on nutrients (FAO, 2018) of the Livestock Environmental Assessment and Performance (LEAP) Partnership, presents a methodology that calculates the allocation of emissions from livestock production to manure and other animal products such as eggs, milk, meat, skin, or fiber.

As manure is often traded at a price that is not necessarily linked to its nutritional value as fertilizer, the study quantifies the value of an equivalent application of mineral fertilizers, which the farmer would apply in order to achieve the same crop yields. The proposed method is illustrated and discussed with two case studies, looking beyond the system expansion approaches for allocation that are in line with LEAP guidelines.

Recognizing the nutrient value in manure and thus, treating manure as a co-product, may encourage the livestock farmers to ensure that nutrients in manure at excretion are not lost during manure management but increase the nutrient equivalent value of the product.

Read the FAO LEAP guidelines on nutrients use efficiency and impact assessment