INRA Feed Unit System for Ruminants: a new ‘Red Book’

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The INRA feed unit system for ruminants, widely adopted in France and several countries, has been regularly updated. But some limits appeared regarding emerging challenges for animal nutrition: prediction of feed efficiency, product quality, effect of feeding on animal health and emissions to the environment. It also did not properly cover the use of low-quality or high-concentrate diets. To address these issues, a group of INRA researchers involved in ruminant nutrition was estabished in 2010 to work on the ‘Systali’ project. The system has been renewed using meta-analyses (large data bases of digestion, metabolic balance and animal performance, representative of the major feeding practices), and modelling with evaluations and simulations. The dietary supply model has been renewed to account for digestive interactions and flows of individual nutrients (VFA, glucose, AA, LCFA). Feed values are no longer additive and depend on the final ration. Requirements have been updated to account for variability in metabolic efficiency and new ration values, and various productive and non-productive animal responses to diets have been modeled. The main advances are presented in a new ‘Red book’, the ‘INRA Feed Unit System for Ruminants’ (Wageningen Academic Publishers), organised in 4 parts. The first two parts present biological concepts and equations (with their field of application and statistical precision) used to predict intake (including at pasture) and nutrient supply (Part 1), animal requirements and responses to diets (Part 2). They apply to net energy, metabolisable protein and amino acids, but also water, minerals and vitamins. Part 3 presents the use of concepts and equations in rationing with two purposes: (1) diet calculation of a given performance objective; and (2) prediction of the multiple responses of animal to diet changes in the case of dairy and meat, large and small ruminant productions. Part 4 provides tables of feed values, and their prediction. For each part, specificities for tropical and Mediterranean areas are presented. All the equations and concepts will be embedded in the INR@tion software available on the internet for practical use.