The aim of this study was to determine the effects of supplementation of dairy heifers with organic acids or polyphenol-essential oil mixtures on their ability to cope with induced subacute ruminal acidosis (SARA). In each of 3 periods heifers were fed a low starch (LS) diet (NDF 39.8%, NSC 36.4%, starch 24.0% DM) for 2 wk followed by a high starch (HS) diet (NDF 33.6%, NSC 43.2%, starch 30.0% DM) for 8 d. To induce SARA top dressed barley meal was given (0.5–1.5 kg) in the last 5 d of the study. During the HS diet 6 Holstein heifers were randomly assigned to 1 of 3 dietary treatments in a 3 × 3 factorial design: no supplement (Ct), a daily dose of 60 g of fumarate and malate mixture (Fm) or 100 g of polyphenol and essential oil mixture (Pol). Reticular pH values were continuously measured using wireless sensors and compared with pH measurements obtained by rumenocentesis. Fecal pH was measured at 0800, 1400 and 2100 h. Fm led to a lower DMI due to its possible lower palatability. The correlation coefficient comparing the pH values obtained using the 2 methods was 0.83 (P