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The quantification of the main digestive processes in ruminants: the equations involved in the renewed energy and protein feed evaluation systems

INRA Prod. Anim. 26(4) 327-346


1 INRA, UMR791 MoSAR, 16 rue Claude Bernard, F-75005 Paris, France
2 AgroParisTech, UMR791 MoSAR, 16 rue Claude Bernard, F-75005 Paris, France
3 INRA, UMR1213 Herbivores, F-63122 Saint-Genès-Champanelle, France
4 Clermont Université, VetAgro Sup, UMR1213 Herbivores, BP 10448, F-63000 Clermont-Ferrand, France


The evolution of feeding systems for ruminants towards multiple animal response systems requires the updating of the calculation of nutrient supply to the animals to make it more accurate on aggregated units (UF and PDI) and to allow prediction of absorbed nutrients. This updating is based on the building and interpretation through meta-analysis of large databases of digestion and nutrition of ruminants. Different equations involved in the calculation of UF and PDI have been updated, allowing the following: 1 ) predicting the passage rate of particles and liquid depending on the level of intake and the proportion of concentrate, and taking it into account in order to calculate the ruminal digestion of protein and starch from in situ data; 2) taking into account the effects of the main factors of digestive interactions (level of intake, proportion of concentrate, rumen protein balance) on organic matter digestibility, energy losses in methane and urine; 3) calculating in a more accurate way the energy available in the rumen and the efficiency of its use for microbial protein synthesis. This renewed model leads to the conclusion that UF and PDI values of feed vary depending on the diet, the feed table values being only indicative. It is thus possible to predict the nutrient supply on a wider range of diets more accurately and in particular to better address energy x protein interactions.

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