In pasture-based dairy systems, breeding and feeding strategies affect GHG emissions and nitrogen losses

International audienceWhich pasture-based dairy system is the most beneficial from an environmental impacts perspective? The results of the long-term experiment ‘Which cow for which system?’ (WCWS) undertaken at the INRAE experimental farm of Le Pin-au-Haras in Normandy were used to address this question. One hundred and sixty dairy systems were designed from the WCWS trial based on six factors monitored in the experiment, including feeding strategy (low (LFS) with only grass or high (HFS) with less grass, maize silage and concentrates) and breed (Holstein or Normande). Their common objective was to produce yearly 420,000 litres of milk. The CAP’2ER tool was used to determine the greenhouse gas (GHG) emission and the nitrogen losses of each system. The average GHG gross emission was 1.18±0.08 kg eqCO2 l-1 of milk and the average nitrogen balance was 146±10 kg N ha-1. The ‘LFS’ systems and the ‘Holstein breed’ systems had lower gross GHG emissions. The LFS had a higher nitrogen surplus (+7 kg N ha-1) but the nitrogen leaching risk was significantly lower than HFS (-27 kg N ha-1). This comparative analysis highlights the need for environmental trade-offs in the face of the diversity of impacts assessed