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

Shepherd, M., Shorten, P., Costall, D., Macdonald, K.A.
Agriculture, ecosystems & environment 2017 v.236 pp. 285-294
autumn, dairy cows, excretion, farming systems, feed intake, lactating females, lactation, leaching, nitrogen, nitrogen content, nitrogen fertilizers, pastures, stocking rate, summer, urination, urine
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)kgNha−1); stocking rate (2.6 (F) vs. 3.2 (C) cows ha−1); and moving cows off pasture to a stand-off pad for 6h 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.gNL−1) or urine volume (1.98L) 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−1day−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. 190gN cow−1day−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. 585gNha−1day−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 6h 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.