A meta-analysis was performed with a data set of 431 treatment means from 117 trials reported in 107 published peer-review journal reports from 1988 to 2015. The study had 3 steps: (1) examine relationships between chewing activity and selected dietary treatments; (2) determine effects of chewing activity on lactation performance by dairy cows; and (3) develop predictive equations for rumination time (min/d) and milk fat content and yield. For steps 1 and 2, data were analyzed using PROC MIXED of SAS with fixed effects of treatment and random effect of trial. A manual deletion stepwise backward elimination of multiple regressions was performed to generate predictive equations for step 3. Intake of DM was unrelated to eating, rumination and chewing times (min/d; P > 0.90); but negatively related to rumination and chewing times (min/kg of DMI; P = 0.001). Eating, rumination and chewing times were positively related to dietary NDF and forage NDF (FNDF) concentrations. Greater consumption of NDF and FNDF both, when expressed as kg/d or percentage of BW, elicited (P = 0.001) greater eating, rumination and chewing times. Greater eating time reduced (P < 0.05) milk, milk protein, 3.5% FCM and ECM yields; but stimulated greater (P = 0.001) milk fat content. Greater rumination time was associated (P < 0.01) with enhanced milk fat content and yield, tended (P = 0.07) to reduce milk protein content, and was unrelated (P > 0.10) to other lactation performance parameters. Greater chewing time was related (P = 0.001) to greater milk fat content but reduced (P < 0.05) milk yield and milk protein content. Best-fit model to predict rumination time included feed efficiency (kg milk/kg DMI), FNDF (% of DM) and DMI (kg/d). Prediction of milk fat content was best achieved by NDF intake (kg/d) and dietary NDF and FNDF concentrations. Chewing activity was affected by dietary concentrations or intake of NDF and FNDF. Chewing activity influenced lactation performance.