The effect of feeding strategies on enteric and manure methane emissions in dairy cows: evidence from Italian farms

The dairy sector faces increasing environmental challenges, with methane being a major concern due to its role in enteric emissions from livestock. This study explores the impact of various feeding strategies on methane emissions from lactating Holstein cows fed TMR silage-based diets. Data were collected from 36 dairy farms in Northern, Central, and Southern Italy. Four equations for estimating methane emissions were compared to assess whether they behave differently in response to diet variability and sensitivity to dietary changes. The Global warming Potential (GWP) of the diet was calculated as the sum of each feed’s GWP in the TMR. The study also investigated how feeding strategies affect the excretion of volatile solids and methane emissions from manure. A hierarchical cluster analysis categorised diets into homogeneous groups based on (i) their nutritional profile, including feed type, inclusion level, and nutritional characteristics, and on (ii) feed composition. The four diets groups based on feed composition showed no significant differences in methane emissions. Clustering by nutrient composition revealed three categories: ‘High quality’, ‘Medium quality’, and ‘Low quality’ diets. Only the Mills equation detected differences between these nutrient-based clusters. According to this equation, average CH4 emissions were 460.36 ± 46.95 g / d, 18.90 ± 1.57 g / kg DMI, and 12.89 ± 2.83 g / kg FPCM, corresponding to a 5.93% loss of gross energy intake. The low-quality cluster showed the highest emissions, with methane production reaching 485.85 g / d. Notably, this cluster had the lowest methane emissions, equal to 19.47 kg CO₂eq / kg DMI and 14.82 kg CO₂eq / kg FPCM. Despite variations in diet GWP across clusters, ranging from 0.45 to 1.17 kg CO₂eq / kg DMI, no significant differences were observed. The choice of feed type had no significant impact on emissions or GWP in this context. However, the type of equation used influenced the evaluation of feeding strategies. Empirical equations based on single intake variables identified differences in methane intensity but not production, while the Mills equation accounted for both factors. This highlights the importance of accurately estimating enteric methane emissions to improve national greenhouse gas inventories and develop context-specific models for effective mitigation strategies in dairy farming.