Alpha-1-acid glycoprotein (AGP) is an acute-phase protein that may suppress DMI by acting on the leptin receptor in the hypothalamus. Our objective was to characterize plasma AGP concentration and associations with DMI during the transition period. Plasma samples (n = 2,086) from 434 Holstein cows in 6 studies were analyzed on d −21, −12 ± 3, −3, 1, 3, 7 ± 1, 14 ± 1, and 21 ± 1 relative to parturition. Bivariate analysis was used to assess the relationship between AGP and DMI. For significant associations, treatment(study) was added to the model and quadratic associations were included in the model, if significant. Mean plasma AGP concentration (±SEM) was 273 ± 70 μg/mL prepartum, and postpartum was 468 ± 66 μg/mL (d 3), 568 ± 66 μg/mL (d 7), 532 ± 65 μg/mL (d 14), and 457 ± 66 μg/mL (d 21). On d −12, AGP was negatively associated with wk −2 DMI (P < 0.05) and wk 1 DMI (P < 0.05). On d 3, AGP was associated negatively with DMI in a quadratic manner for wk 1 (P < 0.001) and wk 2 (P < 0.05) and linearly for wk 3 (P < 0.001). Day 7 AGP was associated negatively with DMI in a quadratic manner for wk 2 (P < 0.05) and linearly for wk 3 (P < 0.001). Similarly, d 14 AGP was negatively associated with DMI for wk 3 (P < 0.001) and wk 4 (P < 0.01). As d 3 AGP concentration increased over the interquartile range, there was a calculated 1.4 (7.8%), 0.5 (2.8%) and 0.4 (1.9%) kg/d reduction in predicted DMI during wk 1, 2, and 3, respectively. Using bivariate analysis, d 3 AGP explained 15.4% of the variation in DMI during wk 1. Finally, we explored the clinical utility of d 3 AGP to diagnose low DMI, defined as wk 1 DMI more than 1 standard deviation below the mean. Receiver operating characteristic analysis identified a threshold of 480.9 μg/mL providing 76% specificity and 48% sensitivity (AUC = 0.60). These results demonstrate a negative association between plasma AGP concentration and DMI in early postpartum dairy cows, although its diagnostic performance was marginal. Further investigation into whether AGP directly suppresses DMI in dairy cattle is warranted.