Dairy cows are typically fed high concentrate diets. This feeding practice reduces chewing activity and leads to a high risk of subacute ruminal acidosis (SARA). The excess of concentrates in the diet may further deteriorate cow health and productivity. Because of their potential to modulate ruminal pH, phytogenics (PHY) and autolyzed yeast (AY) may counteract negative consequences of high-concentrate diets. This study investigated, if supplementing concentrate-rich diets with PHY and AY modulates chewing behavior and reticular pH. Eight ruminally cannulated nonlactating Holstein cows were arranged according to an incomplete double 4 × 3 Latin square design with 4 runs and 3 treatments (PHY (Digestarom Dairy, Biomin Holding GmbH), AY (Levabon Rumen E, Biomin Holding GmbH) or no additive (CON) (n = 8 per treatment). The treatments were mixed and fed with the respective concentrates. During each run cows were fed a pure forage diet (FD1) before receiving a 65%-concentrate diet for one (CONC1) or 2 (CONC2) weeks, divided by a week FD2. Chewing activity was measured using noseband sensors (RumiWatch System, ITIN + Hoch GmbH) for 2 d during FD1, CONC1 and CONC2, while ruminal pH was evaluated continuously using wireless pH sensors (eCow, Decon). Statistical analysis was performed using the MIXED procedure of SAS. For each variable tested, the time (feeding phase, d or h) and the treatments (CON, PHY and AY), as well as a possible interaction between them, were considered as fixed effects. Cows receiving AY had a higher feed intake during CONC1 and spent 1 h/d more eating than CON-cows (P = 0.02). At the same time PHY increased ruminating time by 1.5 h/d (P = 0.04) and enhanced the number of chews/bolus (P = 0.01). In agreement the time of ruminal pH <6.0 of cows fed PHY was decreased by up to 4 h/d (P < 0.05). Data suggests that inclusion of PHY can reduce negative effects of high-concentrate diets by increasing ruminal pH. Furthermore, PHY had a positive effect on ruminating time and chewing behavior.