1. Agroscope Liebefeld-Posieux Research Station ALP; 1725 Posieux Switzerland
2. ETH Zurich, Institute of Animal Sciences; 8092 Zurich Switzerland
3. Agroscope Reckenholz-Tanikon Research Station ART; Zurich Switzerland
4. Chemistry and Biochemistry Laboratory, School of Agriculture, Policy and Development; University of Reading; Reading RG6 6AT UK