Dairy Farming: Feed, Wind and Temperature Influence Ammonia and Nitrous Oxide Emissions

Agriculture is aiming to reduce greenhouse gas and ammonia emissions. Agroscope showed that for dairy cattle housing, feed composition plays a role in these emissions as well as wind and temperature.

Apart from carbon dioxide (CO₂), the most powerful anthropogenically emitted greenhouse gases are methane (CH₄) and nitrous oxide (N₂O). In Switzerland, around 64% of N₂O emissions and 83% of CH₄ emissions were from agriculture in 2020. Ammonia (NH₃) emissions accounted for around 94% of agricultural emissions in 2019, primarily from livestock farming. The Swiss agricultural sector aims to reduce NH₃ emissions by around 40% and greenhouse gas emissions by at least one-third. Measures for feed optimisation start at beginning of the production chain and can be implemented in practice without the need to convert existing housing.

Greenhouse gas and NH₃ emissions under practical conditions

Our study quantifies the emissions (NH₃, N₂O, CH₄, CO₂) in two separated but structurally identical compartments of a naturally ventilated cubicle housing system for lactating dairy cows. The cows in one compartment were fed a diet with 116g crude protein (CP) per kilogram of dry matter (DM), in the other compartment with 166g CP kg⁻¹ DM. The diets fed in both compartments were subsequently switched around for a second six-day measurement phase.

Protein-reduced diet leads to lower ammonia and nitrous oxide emissions

The results showed that, in addition to outside temperature and wind speed, diet is a relevant factor influencing NH₃ and N₂O emissions. Higher temperatures or wind speeds led to a significant rise in NH₃ emissions. Lower levels of CP in the diet can reduce dairy-cow nitrogen excretion and hence ammonia and nitrous oxide formation potential. On average, there was a 46% reduction in NH₃ and an almost 20% reduction in N₂O emissions per animal when the lower rather than the higher-CP diet was fed. DM intake and milk yield decreased slightly in cows fed the lower-CP diet. Regardless of whether the emissions related to livestock unit (LU), DM intake or energy-corrected milk yield, the effects of diet, temperature and wind speed in the housing on NH₃ emissions were highly significant. Furthermore, a strong correlation between dietary CP content, urinary N excretion and milk urea content was observed.

CH₄ emissions are also affected by diet

The composition of the ration can also influence CH₄ emissions. The differences in CH₄ emissions point to a significant influence of the feed which is actually attributable to crude fibre content rather than crude protein content. In terms of CH₄ emissions, therefore, both dietary crude fibre content and DM intake must be taken into account.