Cow’s use of feed can now be gauged
Milk comes from cows, no surprises there, but how efficient are cows at converting feed to milk? A Lincoln University student has developed a method to measure how efficient the animals are
A goal for all Kiwi dairy farmers is the maximisation of milk output.
But what is the quality of this milk and how much feed does it take a pint.
Lincoln University doctoral candidate Long (Paul) Cheng of the Faculty of Agriculture and Life Sciences is trying to answer these questions.
Mr Cheng has developed a simple non-invasive method to measure the efficiency with which cows convert feed protein to milk protein. ‘‘Inefficient use of feed protein by cows results in high levels of nitrogen in their urine,’’ he said.
‘ ‘ This can lead to increased nitrate leaching to groundwater and elevated levels of nitrous oxide released to the atmosphere.’’ 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,’’ Mr Cheng said. ‘‘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.
Mr Cheng’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,’’ he said.
Mr Cheng 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 used the nitrogen from their diets.
His technique will aid researchers by providing a simple way to measure nitrogen fractionation in milk.
Nitrogen use efficiency 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. Mr Cheng’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, his 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 said the challenge now was ‘‘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’’.
The research is funded by the Foundation for Research Science and Technology’s Dairy Systems for Environmental Protection project.
GRASS TO MILK: A Lincoln University doctoral candidate has developed a test for how efficiently cows turn feed into milk.