The effective ruminal degradability (ED6_N) and true intestinal digestibility (dr_N) of nitrogen measured in sacco are used to describe the nutritive values of feedstuffs in the INRA 2018 feeding system for ruminant and its rationing software (INRAtion®V5). In the perspective to move from in sacco to in vitro tests, a global sensitivity analysis (GSA) was conducted to measure the sensitivity of the INRAtionV5 to variations in input variables: gross energy (GE) and crude protein (CP) contents, organic matter digestibility (OMd), ED6_N and dr_N. We used Sobol’s indices that calculated input’s contribution to each output with interactions among inputs (Sti). The GSA was performed with 6 diets varying according to forages (corn silage, grass fresh/hay/silage) and concentrates (cereals and oil seed meals). These diets were formulated for a multiparous dairy cow at week 14 of lactation, and contained 14 to 18% CP. Then, 10,000 quasi-random samples of the 5 input variables were generated per diet using Sobol’ sequences. Variations on predicted dry matter intake were on average mainly due to GE (StGE=53±5.3%), but with grass hay and grass silage diets, OMd was the main contributor (StOMd=52 and 51%, respectively). The contribution of OMd was the highest for milk yield (MY; 63±11.0%), protein yields (MPY; 68±8.7%) and protein contents (MPC; 79±7.2%). With grass silage and fresh forage diets (14% CP), ED6_N was the second contributor to MPY (24 and 16%, respectively) and MY (2 and 18%, respectively). Urinary N flow was most affected by CP (60±8.4%), and faecal N flow (FN) by GE (35±9.6%) and OMd (33±14.4%). The ED6_N was the second contributor to FN in corn silage diet (33%) and grass hay diet (41%). Interaction among the input variables was the highest (>35%) on MPY and MY with grass hay diets with oil seed meal, but was the lowest (<5%) with grass hay diet without oil seed meal. In conclusion, with diets containing 14 to 18% CP, protein-related inputs less contributed than energy related inputs to changes in DMI and milk production. But with 14% CP diets, production responses are sensitive to ED6_N.