Urine sensor-based determination of repeatable cow urination traits in autumn, winter and spring

Nitrogen (N) excreted in urine by grazing ruminants is the main source of N loss from pasture-based agriculture. In this study we used cow-attached urine sensors to measure the between-cow, between-day, within day diel and between-season patterns in the urination events from grazing cattle. The urine sensor was deployed for four days to estimate the time, frequency, duration, flow rate, volume, N concentration and N load of individual urination events from 13 to 15 cows per trial in autumn, winter, and spring. Repeat measurements were also obtained on cows in the autumn, winter, and spring trials. There was seasonal variation in the urination traits, with lower N output per event and N output per day in autumn. The urination events exhibited significant diel patterns, with a 2 to 5-fold diel variation in all urination traits. The diel patterns for each urination trait also displayed three distinct peaks and three distinct minima at times that were approximately consistent between seasons. We also established between-cow variability in the diel amplitude of each urination trait. Low amplitude diel cows are likely to have a lower N loss potential as they excrete a lower proportion of very large N load events, which far exceed the ability of pasture to utilize the excreted N. The duration of urination can predict event volume (RMSE = 0.8 L) and the combination of duration and frequency can predict event N load (R2 = 0.67). The between-cow variability in the urination event traits had coefficients of variation that range from 10 to 20% (ratio of standard deviation to the mean), and the between-day variation in the urination traits ranged from 7 to 20%. There is therefore potential to identify cows that for a fixed N intake excrete a lower N load per urination event over an entire season.