Assessment of enteric methane emissions in three Italian dairy cattle breeds using Dairy Herd Improvement (DHI) data

In recent years, the dairy sector environmental impact, particularly methane (CH4) emissions, has drawn significant attention due to its role in global warming. Establishing context-specific emission factors baselines is essential for accurate inventories, evaluating mitigation strategies tailored to regional conditions. Our study evaluated the IPCC Tier 2 approach for estimating CH₄ emissions, comparing results based on default values and diet-specific data across three dairy cattle breeds in Italy. Data were collected from 138 farms housing Holstein, Red Pied, and Brown Swiss breeds, encompassing 8,172 lactating cows, 7,163 heifers, and 1,172 dry cows. Longitudinal DHI data included information on milk yield, fat and protein content (FPCM), and herd composition. Dietary data encompassed detailed daily ration composition and feed quantities for each animal category. Enteric CH₄ production (MeP), yield (MeY), and intensity (MeI) were estimated for three dairy cattle categories across three breeds using two methods: (i) the IPCC Tier 2 (2021) approach with default values for diet digestibility (DE), NDF and daily Gross Energy Intake (GEI) estimated via an energy model, and (ii) the IPCC Tier 2 (2021) approach incorporating specific diet data for DE, NDF, and GEI. Subsequently, CH₄ farm intensity (kg CH₄ per herd / kg FPCM) was evaluated. Mean differences were assessed with Kruskal-Wallis test. The study revealed significant differences (p < 0.05) in emissions among the breeds. Holstein cattle exhibited the highest MeP (443.5 ± 55.6 kg CH4 / d) emissions but the lowest MeI (13.9 ± 3.8 kg CH4 / kg FPCM), whereas the Red Pied showed the lowest MeP (411.0 ± 65.3 kg CH4 / d) emissions but the highest MeI (19.5 ± 6.3 kg CH4 / kg FPCM). A similar trend was observed in CH4 farm intensity (CH4herd / kg FPCM; 21.2 ± 6.0 in Holstein and 30.0 ± 9.9 in Red Pied). The estimation method significantly influenced CH4 emission estimates. In Holstein cattle, lactating cows demonstrated higher MeI, while dry cows had higher MeP, and heifers exhibited higher MeP and MeY. Additionally, farm intensity was higher in this breed. For Red Pied cattle, higher emissions (MeP, MeY) were observed in lactating cows and heifers; and MeP only in dry cows, also displaying increased farm MeI. The findings of this study have the potential to facilitate a more accurate quantification and monitoring of enteric CH4 emissions at the farm level in the Italian scenario.