Published online by Cambridge University Press: 24 November 2017
In ruminants, daily urinary excretion of purine derivatives (PD) reflects the absorption of microbial purines and can be used as an index of microbial protein supply (Chen, Ørskov and Hovell, 1991). The application could be extended to farm conditions if measurements based on spot urine samples or plasma could serve as an alternative index. The objective of this study was to examine whether PD concentrations in spot urine or plasma samples vary diurnally during a given feeding regime and if they reflect differences in daily PD excretion induced by varying feed intake.