Modeling relationships between dietary intake and net fluxes of energy nutrients across splanchnic tissues in ruminants

The INRA feeding system for ruminants was established to adjust diets to the production genetic potential of animals, in order to enhance productivity. Presently, the stakes of the industry in animal production and of animal nutrition have diversified. They include performance objectives but also efficiency, quality of products and reduction of animal wastes, in the respect of animal well fare and health. Prediction of these multiple responses implies to know the amount and the nature of nutrients available to the organism. The objectives were thus to establish empirical prediction models of 1) net portal appearance (NPA) and 2) net splanchnic release (NSR) of energy nutrients. Meta-analyses methods were applied on data from the FLORA data base, which is an exhaustive compilation of publications dealing with splanchnic fluxes in ruminants. Stables models were obtained for intakes up to 30 g DM/d/kg BW and for diets which included less than 70% concentrates. The models allowed to predict the total volatile fatty acids (VFA) and beta-hydroxybutyrate (BHBA) NPA from the amount of ruminally fermentable organic matter (RfOM), the profile in VFA from the nature of RfOM, the amino acids (AA) NPA from the protein digestible in the small intestine and the lactate and glucose NPA from the amount of starch digested in the rumen and the small intestine respectively. The NSR of each VFA and AA can be predicted from their NPA. The lactate NSR was predicted from its NPA and propionate NPA or from the energy balance of the animals, the BHBA NSR from the RfOM and the animal energy balance. Finally, the glucose NSR was predicted by its precursors' hepatic supply.