Towards revised dietary phosphorus recommendation for ruminants

Abstract

To take into account the environmental challenge, recommended phosphorus allowances have to satisfy refined animal requirement assessments as well as the control of pollutant loading in the environment. In the factorial approach, the most sensitive parameters which are maintenance requirement (MR) and true absorption coefficient (TAC), were re-considered trough a quantitative treatment of a bibliographic database and some recent experimental results. MR is strongly related to phosphorus salivary flow and its variations ; consequently, dry matter intake appeared to better estimate MR than body weight. In the future, the quantification of rumen micro-organisms in phosphorus faecal excretion may allow to assess MR more accurately. Up to now, the TAC values currently used for the calculation of recommendations are way below the experimental data ; important variations were also observed between feedstuffs. Future nutritional standards may adopt specific TAC values for feedstuffs or at least for feedstuff groups. Phosphorus release kinetics in the rumen were highly variable among feedstuffs, this suggests that there are differences in phosphorus availability for the rumen ecosystem. With the hypothesis of a significant decrease of phosphorus supply to ruminants, the effect of these discrepancies upon micro-organism efficiency must be investigated.