The objective of this study was to quantify the effects of supplementing early-lactation cows with a dry pure glycerol product, delivered through the automated milking system (AMS) concentrate, in the first 21 d in milk (DIM) on metabolic markers, milking behavior, and milk production. In 5 commercial AMS dairy herds, 389 dairy cows were randomly assigned, controlling for parity, 21 d before expected calving to 1 of 2 treatments, within farm: (1) control group (CON) receiving the standard AMS pellet (n = 213) from 1 to 150 DIM, or (2) glycerol group (GLY) receiving the treatment AMS pellet (n = 176) formulated to deliver 250 as fed g/d of glycerol product from 1 to 21 DIM (mean actual = 249 g/d dry matter [DM]), then they received the standard AMS pellet from 22 to 150 DIM. Across all farms, cows were fed partial mixed rations (PMR) that were similar in ingredient and nutrient composition. One prepartum blood sample and 5 postpartum blood samples were collected from each cow to determine serum nonesterified fatty acids (NEFA), blood β-hydroxy butyrate (BHB), and blood glucose concentrations. Cow body condition score (BCS) was recorded every 21 d from -21 to 63 DIM. Data were collected and analyzed for the treatment period (1 to 21 DIM) and a follow-up period (22 to 150 DIM). There was no detected treatment effect on serum NEFA concentrations in the first week of lactation. There was a treatment by time interaction for blood BHB and blood glucose, where GLY cows tended to have increased BHB concentrations at 5 DIM and had decreased glucose concentrations at 9 and 12 DIM. There was an interaction of BCS with treatment on the incidence of BHB ≥1.2 mmol/L, whereby over-conditioned CON cows (BCS ≥3.5) were 3.5x more likely to have a high BHB test than CON cows with normal prepartum BCS. During the treatment period GLY cows had 0.1 ± 0.05 more successful milkings/d, were delivered 0.27 ± 0.05 DM kg/d more AMS concentrate and tended to yield 0.8 ± 0.47 kg/d more milk. During the follow-up period GLY cows had 0.1 ± 0.04 more successful milkings/d, were delivered 0.18 ± 0.06 DM kg/d more AMS concentrate, and yielded 1.5 ± 0.53 kg/d more milk than CON cows. Glycerol supplementation allowed cows to maintain better BCS, as GLY cows lost less BCS from calving to 63 DIM than CON cows. Overall, the results of this study demonstrate that supplementing pure glycerol through the AMS concentrate for the first 21 DIM can reduce BCS loss in early lactation, improve milking behavior, and increase milk yield to mid lactation.