Sensors for detecting and logging spatial distribution of urine patches of grazing female sheep and cattle
Urine excreted in patches by grazing livestock accounts for much of the nitrogen (N) loss to the environment in grazing systems. These losses arise mainly through N leaching to ground water and gaseous losses to the atmosphere. Models of grazing systems ideally require data on urination frequency, N load in each urination event and spatial distribution patterns of urine. To date there has been a lack of suitable equipment for obtaining information on urination characteristics of grazing animals. This paper describes a urine sensor that detects and logs each urination event of female sheep and cattle. A thermistor suspended below the vulva continuously measures ambient temperature except when urine passes over it, causing the temperature to rise to near body temperature. Field validation showed 85% and 78% of sensor-detected urination events by sheep and cattle sensors, respectively, were seen by the observer. Some of the urination events identified by the sensor but not seen by the observer were confirmed by video footage. For cattle, only one observed urination event was not detected by the urine sensor, giving a 4% error rate of detection. Daily urination frequencies (ewes: 13–23 events day−1; cows: 11–26 events day−1) were similar to published data for these species. A custom-made GPS unit worn on the rump of the ewe and on the collar of the cow logged animal position continuously so that urine patch position could be determined. Examples of urine distribution patterns by ewes and beef cows in large, hilly paddocks clearly show campsite locations where a disproportionate number of urination events occurred. For sheep, the correlation between time spent in an area and the number of urination events in the same area was r = 0.82, but this correlation was weaker for cattle (r = 0.54).