a1 University of Waikato, Hamilton, New Zealand
A study of the fractionation of nitrogen isotopes in the diet by cattle is described and the results discussed.
Compared with the diet, urine had a lower ratio of 15N to 14N, but faeces, blood and milk all had a higher ratio.
It is argued that the use of natural 15N as a tracer in grazed ecosystems is more complicated than was at first thought.
(Received May 03 1977)
p1 Present address: Kuakura Agricultural Research Centre, Private Bag, Hamilton, New Zealand.