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Published online by Cambridge University Press: 22 November 2017
It has long been recognised that there is a strong positive relationship between the level of absorbed (microbial) purines and purine derivative excretion in the urine. We have used estimates based on urinary allantoin N excretion (AN) to investigate some of the factors influencing the energetic efficiency of microbial yield from the rumen (E). Figures 1 and 2 illustrate the model that has been adopted.
It has been tentatively assumed that, at reasonable levels of intake, exogenous purine supply exceeds “a” moles (Figure 2) so that purine salvage is saturated (Condon & Hatfield, 1970), de novo synthesis inoperant (Condon, Hall & Hatfield, 1970) and the net endogenous contribution to AN negligible. In these circumstances AN will be linearly related to microbial (purine) yield from the rumen.