Supplementation of live yeast (LY) in the diet is an interesting practice to limit the negative effects of SARA. Measurement of ruminal redox potential (E_h) has been shown to be a tool to understand the mode of action of LY in rumen. The objective of this study was to quantify the effect of LY (5g/d of Saccharomyces cerevisiae, 10¹⁰ cfu/g DM, CNCM I-4407, Phileo Animal Care, France) on ruminal E_h of lactating and dry cows via quantitative analysis of data from 16 experiments (including 27 LY treatments) conducted by our research team. A total of 575 kinetics (each established from morning feeding to 8 h after) of ruminal E_h and pH were gathered together. Yeast effect on ruminal E_h, pH, VFA and ammonia concentration was tested qualitatively (control vs. LY). The relationship between response of ruminal E_h (difference between yeast treatment and control group) and that of control group was analyzed by a liner model. Thereafter, the relationships between response of E_h and response of VFA and NH₃ concentration were also analyzed by liner model. In lactating cows, addition of LY significantly decreased ruminal E_h (from – 173.5 to – 186.2 mV, P < 0.001) and increased pH (from 5.94 to 6.11, P < 0.001) and total VFA content (from 92.3 to 99.2 mM, P < 0.001). In dry and lactating cows, analysis of relationship between E_h response and E_h of control groups showed that the regulation of ruminal E_h by LY would be particularly efficient when risk of digestive disorder is high i.e., E_h control > –195.7 (E_h response = – 72.4 – 0.37 E_h control, n = 27, P < 0.01, R² = 0.33, RSD = 14.6). Moreover, E_h response is associated with the increase of VFA content response (E_h response = – 8.2 – 1.63 VFA response, n = 20, P < 0.001, R² = 0.57, RSD = 12.2) and the decrease of ammonia content response (E_h response = – 6.5 + 0.41 NH₃ response, n = 18, P < 0.05, R² = 0.34, RSD = 15.9), which suggest an improvement of ruminal fermentation by LY.