The May animal article of the month is entitiled ‘Quantification of the main digestive processes in ruminants: the equations involved in the renewed energy and protein feed evaluation systems.’

Feed unit systems (FUS) have been a major factor of progress in livestock production for calculating optimal diets. For more than a century and a half, these systems have been periodically updated to take account of advances in scientific knowledge and new demands of farm to fork chains. In recent years the production of knowledge on the nutrition of ruminants has grown exponentially. However, limits to FUS emerged during the last decades with respect to the new challenges in animal nutrition, i.e. prediction of feed efficiency, product quality, and the impact of feeding practices on animal health and emissions to the environment. They also did not properly cover the use of low-quality or very nutrient-rich diets. To address these issues, INRA initiated a revision of it’s ruminant FUS in 2010 (Systali).

The French FUS has been renewed using meta-analyses on large data bases of digestion and nutrition in ruminants receiving diets representative of the major feeding practices. The consistency of the numerous equations issued from meta-analyses has been validated through a mechanistic model of digestion.

Most of the equations were targeted at the calculation of net energy (UF) and metabolisable protein (PDI) allowing : 1) the prediction of the outflow rates of particles and liquids depending on the level of intake and the proportion of concentrate, and the use of this in the calculation of ruminal digestion of protein and starch from in situ data; 2) to take 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) a more accurate calculation of the energy available in the rumen (fermented organic matter) and its partition between the microbial protein synthesis and volatile fatty acid production and profile. Beyond the UF and PDI values, prediction of absorbable glucose and fatty acids in the small intestine were calculated. Moreover all these equations were included into an online tool (“Systool”) for easy calculation, from feed data, of the net dietary supplies of energy, protein and other nutrients for a given ration.

This global digestive model is used to update the requirements and to predict animal responses. In this renewed model, UF and PDI values of feedstuffs, as well as their new nutritive characteristics, depend upon the composition of the complete diet and the intake level. Consequently, standard feed table values can be considered as being only indicative. Nevertheless, the new feed tables have been extended to include not only temperate feedstuffs but also those from Tropical and Mediterranean areas. It is thus possible to predict the nutrient supply from a wider range of feed and diets more accurately, in particular better integrating the energy x protein interactions occurring in the gut. The gain of accuracy from the revised FUS will be profitable via a better diet formulation for lactating and growing ruminants.

Ultimately, all these equations and concepts combined with predictions of requirements and responses will be embedded in the INRAtion software available on the Internet for practical prediction of the multiple responses of animal to diet changes in the case of dairy and meat, large and small, ruminant production.

This paper is freely available for one month

Title: Quantification of the main digestive processes in ruminants: the equations involved in the renewed energy and protein feed evaluation systems.
Authors: D. Sauvant, P. Nozière