Using a urine sensor to estimate nitrogen excretion by lactating dairy cows in Australian grazing systems

A.Ahmed1, S.R Aarons2

1 School of life sciences, Latrobe University, Bundoora, VIC, 3083, [email protected]

2 Agriculture, Research and Development, Department of Economic Development, Jobs, Transport and Resources, Ellinbank, Vic, 3821, [email protected]

Abstract

Ruminants excrete most of their N intake, with most of the N excreted in urine. As a result, urine is the greatest contributor of N losses to the environment in dairy systems worldwide, due to the high use of N. While quantifying N excretion will assist in the development of improved N management practices, measurement of urinary N is difficult in grazing dairy systems. A urine sensor developed by AgResearch, New Zealand which allows the determination of N concentration (%) and volume of each individual excretion event performed by grazing cows was tested in Australian conditions. Twenty Friesian-cross lactating dairy cows were fitted with urine sensors and data were recorded over a 48 hour period in spring 2014 and late winter 2015. A total of 420 urination events were recorded in this study. Urine volume excreted by these grazing lactating cows ranged from 8.2 to 43 L/day while urinary N concentration varied between 1.2 and 15.7 g N/L, similar to previously reported results. The average urination frequency was 18 times per day and average volume per event was 8.2 L/event. These data also showed that N concentration varies between time of the day and showed higher concentration in the early morning and afternoon.