24 September 2012 New test helps reduce environmental pollution

Animal scientist and PhD candidate, Paul (Long) Cheng, from the Faculty of Agriculture and Life Sciences at Lincoln University has developed a simple technique which has the potential to reduce environmental pollution caused by nitrogen compounds excreted by grazing animals such as sheep and cattle. This is a small part of his doctoral research project.

“Although there are methods available to measure nitrogen excreted by animals they are almost impossible to use with grazing animals because they involve the collection of urine samples over 24 hours for at least five days,” said Paul. “So this is a very time consuming endeavour.

“The current models to predict potential nitrogen excretion were developed from the total mixed ration (TMR) system and are not suitable for applying to grazing ruminants.

“This test is an important advance that will help farmers and others in their efforts to reduce the effects of increased nitrogen run-off from New Zealand pastures and has the potential to be used in other pasture-based grazing systems worldwide,” said Paul.

Nitrogen excretion by grazing animals is caused by the inefficient uptake of nitrogen from feed the animals eat and results in the release of nitrous oxide (a greenhouse gas) and the leaching of nitrate (a nitrogen containing compound) into ground water.

In developing the new model Paul began by measuring the urine nitrogen output from a small number of sheep fed on various feed types then compared these results with those given by a pre-existing computer model for predicting nitrogen output from feed samples.

He then developed a more accurate model for predicting urinary nitrogen output using a newly identified nitrogen metabolism biomarker from blood samples using a spectrophotometric analysis of 15N (a non-radioactive isotope of nitrogen).

When the new method was trialled the 15N measurements combined with dietary nitrogen concentration provided moderately strong predictions of urinary nitrogen excretion.

“This spot sample 15N technique is easy to conduct on a large number of grazing animals such as sheep and it can be used to quantify excretion and provide support on decision making for mitigation strategies against nitrogen run-off ,” said Paul

Paul will now validate the technique using a larger number of animals. He will then refine the technique further by elucidating how the animals’ diets and the animals’ characteristics also contribute to the variation he found in the urinary nitrogen figures.

Reflecting on the development of this technique, Paul acknowledged his research team led by the Professor of Dairy Production, Grant Edwards, and the field assistance provided by PhD students, Guo Yang and Innocent Rugoho from Lincoln University.

These results will be presented at the AAAP (Asian Australasian Association of Animal Production Societies) annual conference in Thailand later in the year. This research is funded by the Dairy Systems for Environmental Protection project; MSI: NZ and Science Innovation Group and Gan Su Agriculture University, China.