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Gaseous emissions (building, storage, pasture) of dairy systems combining or not grazing and housing
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Edité par CCSD ; Wageningen Academic Publishers -
Session 05. International audience. Sustainable dairy farms need to make better use of feed resources, reduce the use of inputs and their environmental impacts, particularly in terms of nitrogen (N) losses. Dairy cattle are largely fed on grazed grass in Western Europe but, at certain times of the year, conserved forages and concentrates may be added to the animal diet. Few studies have investigated the consequences of this combination on the animal’s N use and manure composition. Moreover, inthese situations, animals divide their time between grazing, where urine and solid excreta fall directly onto the soil, and the building, where manure need to be managed and stored, leading to contrasted impacts on the environment. Our project focuses on strategies combining grazed and conserved forages in dairy systems and their consequences on N flows and environmental impacts. Several experiments were conducted to compare animal performance, N use efficiency and gaseous emissions (ammonia and greenhouse gases) of full-housing (FH) vs half-housing-half-grazing (HH-HG) vs full grazing (FG) management systems in spring and autumn 2022. In the FH treatment, cows were housed in mechanically ventilated rooms where they were fed a basic diet of maize silage and concentrates ad libitum. Manure was scraped, collected and transferred to controlled pens. Gaseous emissions were measured in the house and during manure storage by spot air samples, with several methods. In the FG treatment, cows grazed a temporary pasture equipped with an eddy covariance flux tower and several trace gas infrared analysers (NH3, N2O, CH4, CO2, H2O), and ALPHA passive diffusion samplers for NH3 coupled with short-range atmospheric dispersion modelling for the determination of field-scale gaseous emissions. Cows on the HH-HG treatment were housed in a mechanically ventilated room at night (receiving 8 kg DM of the basic diet) and grazed on a temporary pasture during the day (8 hours). The results will contribute to the acquisition of new knowledge on these mixed systems especially in terms of gaseous losses over the whole continuum of cattle feeding and manure management.
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