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Reduction of ammonia emissions on pasture

What is the effect of a low-protein feed supplement on the ammonia emissions from dairy cattle on pasture? To answer this question, the ammonia emissions from two pasture-based feeding systems with dairy cattle were measured and compared between May and October. In the first system (G) the cows fed exclusively on pasture grass, whilst in the second system (M) 25 % maize silage was supplemented. This resulted in a reduced ratio of protein to energy in the M ration, and correspondingly the amount of excreted nitrogen decreased by around 19 %. The intensive rotational grazing allowed to investigate the temporal dynamics of ammonia emissions. A steady increase was observed during the grazing periods, followed by a relatively quick exponential drop afterwards. Overall, emissions showed only a weak seasonal variation, but significantly lower values (– 40 %) for system M than for system G. The results not only confirm the emission factor for pasture used in the Swiss Inventory, but also show that reduced-protein feed can contribute to a reduction in ammonia emissions.

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