Clinical endometritis (CE) is a multifactorial disease of dairy animals. Retained fetal membranes (RFM) and metritis are the major risk factors of CE in dairy cows. Because uterine inflammation affects the profitability of the dairy industry, antibiotics and hormonal therapies are commonly used to mitigate against the disease. However, the One-Health concept aims to reduce antibiotic use in food animals to avoid the emergence of drug resistance or residues in milk or meat. Thus, phytotherapy may represent a good alternative to antibiotics in food animals. Echinops spinosus (E. spinosus) is a natural plant known to have therapeutic, anti-inflammatory, antimicrobial, and wound-healing properties in vitro. The aim of the present study was to investigate the efficacy of E. spinosus as a preventive strategy for CE in dairy cows with other postpartum complications. Holstein–Friesian cows (n = 36) diagnosed with RFM or metritis enrolled in the study were allocated into three groups. One group received antibiotic treatment. Another group received prostaglandin injection (PG). The experimental group received E. spinosus decoction orally. As a control group, eutocic cows (n = 36), without RFM and metritis were included in the study. The efficiency of the treatment was based on the occurrence of CE and improved reproductive outcomes. At 30 ± 2 DPP, CE was diagnosed in 25%, 58.34%, and 75% in antibiotic, PG, and E. spinosus groups, respectively (p < 0.05). There were no differences between the groups at 55 ± 5 DPP (16.67%, 33.44%, and 41.67% in antibiotic, PG and E. spinosus groups, respectively, p > 0.05). The E. spinosus group had the longest open days, lowest conception rate at 150 DPP, and highest number of services per conception. Oral E. spinosus extract is ineffective as a therapeutic for cows at risk of CE. These findings may pave the way for future innovative strategies employing E. spinosus to protect cattle against endometritis.