Blackberry pomace (BBP) is a by-product generated from juice processing that contains skins, pulp, and seeds of the original fruit. Currently, BBP is disposed in landfills. As alternative, we propose BBP as a novel antioxidant-rich feed supplement for dairy cows during the transition period. Thus, the objective of this study was to evaluate BBP as antioxidant-rich feed supplement in transition dairy cows. Using a randomized block design, 24 multiparous dairy cows (blocked by breed) were given 0 (Control), 57 (Low BBP), or 114 g/d (High BBP) of dried BBP as a top dressing to their fed total mixed ration (TMR). Supplementation started 28 d before predicted calving date and ended 28 d post calving. Blood and milk samples were collected on d 0, 1, 3, 7, 14, 21, and 28 postpartum. Besides markers of metabolism, inflammation, and antioxidant status, we measured at d 7, 14, 21, and 28 postpartum serum concentrations of estradiol and progesterone as indicators of follicular and luteal activity, respectively. In addition, we recorded reproductive events after calving. Reproductive data were analyzed using PROC MIXED, PROC GLIMMIX, and PROC LIFEREG in SAS version 9.4. Fixed effects were breed (Holstein, Jersey) and supplementation (Control, Low BBP, High BBP). For repeated-measures, the variance-covariance matrix was modeled using heterogeneous compound symmetry. High BBP cows showed first heat 12 d earlier (P = 0.02), were first bred 15 d earlier (P = 0.04), and were open for 73 d less (P = 0.002) than Control cows, as more cows tended to be confirmed pregnant from their first breeding (P = 0.06). Moreover, High BB cows resumed earlier follicular activity than Control cows, as Control cows did not reach serum estradiol concentrations similar to those of High BBP cows at d 7 until d 28 (treatment x time effect: P = 0.08). Furthermore, High BBP cows tended to have higher serum progesterone concentrations than Control cows (P = 0.08), as High BBP cows reached serum progesterone concentrations indicative of luteal activity at d 21, one week ahead of Control cows. Our results suggest that supplementation with 112 g/d of BBP may accelerate resumption of ovarian activity and improve reproductive performance of dairy cows.