Fiber digestibility (FD) is a main topic on dairy cows rationing. Main effects on FD could be attributed to pH as well as other aspects. The objective of this study was to investigate in high producing cows, the factors that could have a major impact on total-tract fiber digestibility (TTD). A total of 7 studies involving 53 dairy cows and 1364 fecal samples were examined. Performances and rumen parameters of those cows were recorded10d before the fecal sampling. All data were statistically analyzed in JMP (v14.3). K-means cluster analysis was used to detect cows within diet and trial based on higher or lower TTD (HD and LD group respectively). Then cows with variation in TTD due to diet (group V, n = X) were divided from cows with HD or LD constant and independent from the diet (group I, n = X). Mixed model procedure with a factorial arrangement for TTD, with day as repeated measure was used to study HD and LD groups by V or I. LD and HD -V, did not differed in any parameter analyzed, except for milk yield (+1.3kg in HD, P = 0.04). In fact, these differences were related to TMR characteristics (+2.5% of uNDF240h, P < 0.01) in diets fed LD-V. I groups differed in BW (+95kg in HD, P < 0.01) and lactation number (1.5 vs. 3 in LD and HD respectively, P < 0.01). Rumen parameters were characterized by lower rumination and pH on HD-I (−72 min/d and −0.34 pH point/d respectively, P < 0.01). These results showed that diet composition could affect FD, and that differences in TTD within cow led to increasing production and efficiency. On the other hands, when the differences in TTD are linked to the individual cow the main discriminant effect is the cow size and the lactation number, with reflections on rumen parameters such as rumination and pH.