Evaluation of urine excretion from dairy cows under two farm systems using urine sensors

Urine nitrogen (N) is the main source of N leaching from pasture grazed by dairy cows. The aim of this work was to compare urine-N excretion from lactating dairy cows under two contrasting farm systems (Future (F) and Current (C)). The farm systems differed in: annual N fertiliser inputs to the pasture (50 (F) and 150 (C) kg N ha(-1)); stocking rate (2.6 (F) vs. 3.2 (C) cows ha(-1)); and moving cows off pasture to a stand-off pad for 6 h per day in autumn (F). Continuous measurements of urine volume, time of urination and N concentration were made over three days in both early summer and in autumn using urine sensors. There was no difference between the two farm systems in average urine-N concentration (5.5. g N L-1) or urine volume (1.98 L) per urination, over the two sampling periods. There was a trend for more urinations per cow in F system (c. 14.8 vs. 13.5 cow(-1) day(-1), P=0.1), which was primarily attributed to greater feed intake per cow at the lower stocking rate. Estimated daily urine-N production per cow was unaffected by system (average c. 190 g N cow(-1) day(-1)). Despite no difference in urine-N excretion per cow, there was less urine-N deposited per ha in the lower N input F system (504 vs. 585 g N ha(-1) day(-1), P < 0.05). The reduction was due to less pasture consumed (and less N eaten) per ha in the F system. We conclude difference in stocking rate had a greater impact than the difference in feed intake per cow between the two systems. It was estimated that removing cows from the paddock for 6 h per day in autumn would reduce the daily amount of urinary-N deposited onto the paddock by c. 25%, allowing more N to be recycled as effluent. We would expect less N leaching as a result of less urine-N deposition in the F system arising from a combination of lower N inputs and removing cows for periods of the day. (C) 2016 Elsevier B.V. All rights reserved.