Greenhouse gas emissions from milk production: a case study in a farm using the “compost barn system”

Milk production is an important source of greenhouse gases. In 2023, Brazil produced 35,400,000,000 liters of milk (IBGE, 2024). In 2019, Brazil occupied the third position in the world, behind the United States of America and India (Rocha et al, 2024). Quantifying emissions at farms is essential to understanding total emissions of dairy products in order to select production methods and to seek net zero goals. This paper reports the estimation of greenhouse gases at one single farm in the Itapetininga region, São Paulo State, Brazil. The cows are confined in a “compost barn” system and the farm also produces soyabean and corn. The estimation uses the GHG Protocol as a basis, for the reporting year 2022, complemented with life cycle assessment approach to address indirect emissions. For an annual production of 2.343.000 liters of milk, the emissions intensity is 0,644 kg CO2/l if considering only scope 1 and 2, and 0,75 kg CO2/l considering all scopes (cradle-to-gate). Although it is in the low-emissions range, the result it is still higher than other semi-confined and dry-lot confined methods. When taking into consideration simulated land use change emissions, the CO2 emissions at the farm with the compost barn method are almost one fourth of the lower than the at the farm with semi-intensive, pasture-based cattle growing and because the land use for dairy cattle management occupies a smaller area compared to other management systems. This implies that for milk production expansion, if new land is needed, the compost-barn method is preferred. However, additional benefits reported by the farmer with the change to compost barn such as lower negative incidents with cattle and lower inter-pregnancy time could be also taken into consideration in favor of compost barn method.