Defining a functional unit for dairy production LCA that reflects the transaction between the farmer and the dairy processor

The two main functions of dairy farming are to produce raw milk and to generate an economic income for the farmer (Powell et al. in Nutr Cycl Agroecosyst 82:107–115, 2008), both of which drive the downstream value chain. Farm profit is mainly determined by the quantity and quality of milk, and at the same time, dairy farmers have a responsibility for animal welfare and the protection of human health through milk hygiene. When dairy farmers supply milk to a processor, the payment is based on both the quantity and the quality in terms of composition (fat and protein) and hygiene (total bacterial count and somatic cell count). Somatic cell count reflects the health status of the mammary gland and contributes to reduced shelf life and reduced cheese yield and quality, whilst total bacterial count reflects herd health and farm sanitation. The objective of this work was to create a new functional unit for raw milk at the farm gate/ processor gate, which could be used to better capture the economic function of milk, while still reflecting the quality criteria captured by energy corrected milk and fat and protein corrected milk.

Base price-adjusted milk (BPAM) is proposed as a functional unit to capture more of the functions of the transaction between the farmer and the processor. It expresses the volume of milk delivered as the equivalent volume at base price, such that greater milk solids increase the volume and poor hygiene decreases the volume. The BPAM was compared with energy-corrected milk and was tested using a survey of 54 farms in Ireland and eight scenarios compared with the observed values and an “ideal” scenario with no hygiene penalty imposed.

It was found that kg BPAM for the sample of farms was strongly correlated with kg ECM because of the overall hygiene standard from the sample of farms available. For specific farms at specific times, the hygiene properties contributed to the economic function of the milk in a way that could not be captured using energy-corrected milk. The scenario analysis indicated that high levels of biological contamination, if captured in the raw milk functional unit, could increase carbon footprint by > 200%.

It was concluded that BPAM may not be a necessary functional unit for all studies, but those that focused on the farmer and processor perspectives should consider using BPAM because it captures more of the obligatory properties of raw milk than just quality expressed in terms of milk solids.