Urinary nitrogen excretion by lactating dairy cows in Victorian grazing systems

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Master of Agriculture Science by Research to the School of Life Sciences, Department of Anatomy, Physiology and Microbiology, La Trobe University, Bundoora, Victoria.

Thesis with publications.

Grazing ruminants contribute to global warming and air quality degradation through the emission from their excreta (urine and faeces) of NH3, and N2O and to poor water quality due to leaching losses of nitrogen (N) from urine. Dairy cows do not fully utilize all dietary N and excess N in feed is excreted with proportionally more in urine than faeces. Many approaches have been reported for measuring urine excretion by dairy cows for application in models to estimate N losses. The N output from these models depend upon accurate quantification of urinary N excretion to estimate N deposition on farms. However there is limited information in grazing systems to quantify N excretion (number of urination events, urine volume and urinary N) and to define the spatial distribution of urine by the grazing dairy cows within paddocks. Agresearch developed a urine sensor (Urine sensor MKII) that estimates the number of urination events, urine volume and urinary N concentration of each urine events while cows graze. When this urine sensor is coupled with Global Positioning Systems (GPS) sensor, the spatial distribution pattern of urination around farms can be mapped. The research reported in this thesis aimed to trial the Urine sensor MkII on Victorian grazing system dairy cows, to evaluate the feasibility of using this sensor to estimate urinary N excretion and to measure spatial distribution of urine excretion by these cows. The study took place at the Department of Economic Development, Jobs, Transport and resources (DEDJTR) research centre, Ellinbank, Victoria in southeastern Australia during spring 2014 and winter 2015. Ten Friesian cows were fitted with urine, GPS and activity sensor for up to 48 hours in September/October 2015 and another twelve cows with fitted sensor in June 2015 up to 72 hours. A total of 440 urination events were recorded during both study periods and between 8 and 20 number of urination events recorded daily. The urine volume recorded daily ranged between 8.2 and 43 L/day and average urine volume per event was 2.01 L ranging between 0.37 and 8.23 L/event. Urinary N concentration varied between 1.2 to 15.7 g N/L while the urinary N load deposited was between 0.86 and 64.3 g/event. The combined data from urine, GPS and activity sensors revealed that 76% of urination events were recorded within paddocks, 20% in the dairy shed and yards followed by 4% in the walking lane. Urine sensor is a considered good tool to estimate the N excretion by dairy cows in grazing systems. Urine sensor is a considered good tool to estimate N excretion by dairy cows in grazing systems, however further research is required to better attachment techniques of urine sensor to estimate the accurate volume of urine. Future improvements are recommended to reduce the weight, which will help a better attachment to animals. Identification of an activity sensor urination signature will be very useful for rapid identification of CSAs in paddock and on farms.