Consequential-based life cycle assessment of reducing the concentrates supply level in the diet fed to lactating cows in the alpine dairy farming system

This study aimed to assess the consequences of reducing the concentrates supply level (CSL) in the lactating cows' diet on Alpine dairy system's GHG emissions. Consequential-based Life Cycle Assessment (cLCA) was adopted to assess the consequences within the 'dairy_system' (farm plus milk processing) and outside ('expanded_system'). The functional unit was 1 kg of protein and fat (ProtFat). Data (1-year average) originated from 40 dairy farms in the Alps, collected through farm questionnaires during farm visits. Emissions were evaluated without (GWP) and with land-based emissions (crop- (GWP_LULUC_cb) or global-based (GWP_LULUC_gb) method). The feed conversion ratio was computed in terms of potentially human-edible gross energy (HeECR, MJ feed/MJ milk). Three scenarios were explored: 100% (t(0)), 75% (t(1)75), and 50% (t(1)50) of the initial CSL. Impact values for both systems were analysed with a mixed model to test the effect of the scenarios. At 'dairy_system', 1 kg ProtFat caused 19.0 (GWP), 22.9 (GWP_LULUC_cb) and 23.4 kg CO2-eq (GWP_LULUC_gb) at t(0) and HeECR resulted in 0.71 MJ feed/MJ milk. The CSL reduction from t(0) to t(1)75 and t(1)50 significantly increased impact values (2-11%) and decreased HeECR (from -10 to -23%). Considering 'expanded_system', CSL reduction significantly increased GWP (4%) and GWP_LULUC_gb (3%) but decreased GWP_LULUC_cb (up to -4%). In conclusion, cLCA-based approach evidenced that CSL reductions implied diversified effects on GHG emissions, at Alpine dairy system and at food supply level, giving new insights into the challenge of reducing GHG emissions while favouring the decoupling of milk production from the use of human-edible resources.

Automated summary

This study assessed the consequences of reducing the concentrates supply level (CSL) in the diet of lactating cows on the GHG emissions in the Alpine dairy system. The study used a cLCA approach to evaluate the effects within the 'dairy_system' and outside the system ('expanded_system'). The results showed that reducing the CSL had varied impacts on GHG emissions and the feed conversion ratio. The study provides new insights into the challenge of reducing GHG emissions while maintaining milk production.