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Oversupply of dietary copper (Cu) is common among UK dairy herds, but studies on the long‐term outcomes of this oversupply are scarce. A longitudinal study was undertaken to determine the long‐term implications when 80 Holstein‒Friesian heifers with a mean (±standard error) age of 4.1 ± 0.1 months and a mean liveweight of 137 ± 2.4 kg were fed a recommended (R; 16 mg/kg dry matter [DM]) or high (H; 32 mg/kg DM) dietary Cu concentration until 6 weeks prior to calving. Hepatic Cu concentrations in both treatment groups were elevated into the ranges used to diagnose chronic Cu toxicity in cattle at 6.9 months of age (798 ± 46.4 mg/kg DM for H vs. 643 ± 35.4 mg/kg DM for R), with associated evidence of liver damage. Hepatic Cu concentrations then returned to normality but remained higher (p< 0.001) for heifers fed H than for those fed R and were associated with a reduced (p= 0.044) conception rate to first and second services (73.7 ± 8.05% for H vs. 91.2 ± 7.68% for R). This retrospective analysis identified pre‐study liver damage, which may have affected results. Supplying Cu in excess of requirements resulted in liver damage and reduced conception rates.