Preliminary research dosing palmitic fatty acid (PFA) to continuous culture fermenters contradicted meta-analyses reporting improved total-tract NDF digestibility (NDFd). However, previous experiments dosed fat within pelleted feed and may have inhibited general microbial activity. Our objective was to evaluate whether PFA increases NDFd in continuous culture by dosing PFA supplements as a top dress. In the present study, dual-flow continuous culture fermenters were fed one of 4 treatment diets, either a control (CON) diet, or CON with 85% PFA fat supplement top-dressed at 1, 2, or 3% of the total DM fed (L1, L2, and L3, respectively). The CON diet (37.7 g DM/d) was a 50:50 alfalfa:concentrate pellet mix providing 7.4 g CP, 14.8 g NDF, 11.0 g ADF, and 5.3 g starch fed once daily. Each level of PFA provided 0.4 g of additional fat. Fermenters (n = 8) were run in 4 periods of 2 4 × 4 Latin squares, lasting 11 d each with 4 d sample collection. Buffer dilution and solids passage rate were maintained at 7.0%/h and 5.0%/h, respectively. Data were analyzed using a mixed model with fixed effect of treatment, random effects of fermenter and period, and repeated sampling day. The addition of PFA increased NDFd quadratically (P = 0.02; CON: 44.3, L1: 45.9, L2: 45.8, and L3: 44.8%) and addition of PFA tended to increase ADF digestibility quadratically (P = 0.06; CON: 49.3, L1: 50.0, L2: 50.1, and L3: 48.3%). Starch digestibility (Avg. = 97.9%) was unaffected (P > 0.20) by treatment. Molar proportion of acetate and propionate were cubically affected by dose (P ≤ 0.01) and isovalerate tended to be cubically affected (P = 0.08) but varied no more than 0.1 over all dose levels. No other VFA were affected by dose (P > 0.20). Bacterial N flow was not affected (P > 0.20) by dose, accordingly, bacterial N yield per NDF or ADF digested (g/kg) tended (P = 0.06) to be quadratically affected by PFA dose. There was no effect (P > 0.20) of dose on the percent bacterial N from ammonia (Avg. = 69.2%). The present study replicates previous PFA effects on NDFd - indicating potential for this gain to occur within the rumen. Since PFA did not increase bacterial N yield nor efficiency, microbiome analysis may elucidate community shifts.