Measuring environmental impact of cows

Measuring environmental impact of cows

Maximising milk outputs has been the target for New Zealand dairy farmers over the past few decades.

Lately, however, due to increased public concern about the impact of animal production on environmental pollution, more attention has been given to measuring the efficiency with which cows convert feed nitrogen into milk or meat.

Lincoln University doctoral candidate Long (Paul) Cheng of the Faculty of Agriculture and Life Sciences, is developing a simple non-invasive method to measure the efficiency with which cows convert feed protein to milk protein.

“Inefficient utilisation of feed protein by cows results in high levels of nitrogen in their urine,” says Paul.

“This can lead to increased nitrate leaching to groundwater and elevated levels of nitrous oxide released to the atmosphere.”

Up until now, work in this field has been restricted by the inability to make accurate measurements of the efficiency of individual animals.

“So far, my results look promising,” says Paul. “They have provided strong support for the hypothesis that dietary protein levels influence the distribution of different forms of nitrogen within the cows’ systems, and hence can ultimately impact on nitrate levels in the soil, via urine excretion.

Paul’s method is based on the phenomenon of nitrogen isotopic fractionation in ruminants in which two different, naturally-present, non-radioactive isotopes of nitrogen (14N and 15N) are found either in the milk (as protein) or the urine (as waste).

“The research technique needed to be suitable for large numbers of animals, because it can be used in conjunction with DNA technology to help farmers select cows that use their feed more efficiently,” says Paul.

Paul fed the cows in his study diets with different levels of protein and collected milk, faeces and urine and analysed these for the two isotopes of nitrogen to measure how efficiently the cows utilised the nitrogen from their diets.

His technique will aid researchers by providing a simple way to measure nitrogen fractionation in milk.

Nitrogen Use Efficiency (NUE) can be increased in a number of ways, such as by breeding improved grasses, by the genetic selection of cows, and by feeding animals more balanced diets. Paul’s research is part of an increasingly multi-disciplinary approach to addressing environmental issues in ruminant systems that involves researchers in plant breeding, animal breeding and animal nutrition.

Reflecting this approach, Paul’s PhD supervisors include Professor of Dairy Production Grant Edwards and Dr Alastair Nicol from Lincoln University, and Dr Richard Dewhurst from the Animal Bioscience Centre of Teagasc, Ireland.

Professor Edwards says the challenge now is “to understand the basis of these differences in nitrogen partitioning to elucidate the way in which isotopes of nitrogen fractionate in the rumen and liver.”

This research is funded by the Foundation for Research Science and Technology’s Dairy Systems for Environmental Protection project.

ENDS

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