Ammonia and greenhouse emissions from cow's excreta are affected by feeding system, stage of lactation and sampling time

Decomposition of dairy cows' excreta on housing floor leads to ammonia and greenhouse gases production, yet factors affecting total emissions have not been fully disclosed. This work aimed to assess the impact of lactation stage, feeding system and sampling time on gaseous emission potential of cow's faeces and urine in laboratory chambers systems. Individual faeces and urine were collected from two groups of four cows, at peak and post peak lactation, from three commercial farms with distinct feeding systems: total mixed ration (TMR), total mixed ration plus concentrate at robot (TMR + robot), and total mixed ration plus concentrate in automatic feeders (TMR + AF). Samples were collected before a.m. (T8h), at middle day (T12h), and before p.m. (T17h) milking. In a laboratory chambers system, faeces and urine were mixed in a ratio of 1.7:1, and ammonia and greenhouse gases emissions were monitored during 48-h. Cumulative N–N2O emissions were the highest in TMR + robot system, post peak cows and sampling time T17h. An interaction between stage of lactation and sampling time was detected for N–NH3 and N–N2O (g/kg organic soluble N) emissions. Post peak cows also produced the highest cumulative N–NH3 emissions. Overall results contribute for the identification of specific on-farm strategies to reduce gaseous emissions from cows' excreta. •Feeding systems, stage of lactation and sampling time altered GHG and NH3 emissions.•Emissions of N–N2O were highest at TMR + robot and of N–NH3 at TMR and TMR + AF systems.•Higher cumulative N–N2O and N–NH3 emissions were observed in post peak lactation.•Excreta collected at T17h led to the highest N–N2O cumulative emissions.