Two experiments were conducted to determine the effects of sustained -release copper (Cu) boluses on growth and reproductive traits of beef bulls. Two groups of bulls were used in consecutive years (n=26 in experiment 1; n=20in experiment 2). Bulls in each experiment were allotted by weight and breed into two equally numbered treatment groups (control (C); treated (T)). Bulls were housed together and offered a balanced diet containing 9 ppm Cu for an ADG of 1.4 kg. Treated bulls in each experiment were given 1 Cu bolus (Cupra,® Pitman-Moore, Mundelein, IL in experiment 1; Copasture â ¢ Copasture- 25 bolus Schering-Plough, Kenilworth, NJ in experiment 2). All bulls were bled, had blood samples taken and had scrotal circumferences (SC) measured on d 0,28,56,84,112, and 140. Blood was collected via jugular venipuncture to determine serum Cu and plasma ceruloplasmin (Cp) concentrations. Breeding soundness examinations (B S E) were conducted on all bulls on d 140 and 185 in experiment 1 and d 168 in experiment 2. Body weight and SC were not affected by treatment in either experiment (P > .05). Serum Cu and plasma Cp concentrations were not affected by treatment in experiment 2 (P > .05). Serum Cu was higher for the T bulls on d 56, 84, and 112 in experiment 1 (P < .05). All serum Cu concentrations for both experiments were within the normal range for cattle. Plasma Cp concentrations were recorded only for d 1, 112, and 140 in experiment 1 and were significantly higher for the C group on d 112 (P < .05). There were no significant effects of treatment on the results of the BSE (SC, percentage of normal sperm, progressive motility, and primary or secondary abnormalities) in either experiment. These data suggest that the Cu bolus in experiment 2 had no effect on body weight gains, SC, serum Cu and plasma Cp concentrations, sperm normality, progressive motility, and primary and secondary abnormalities. These data also suggest that the Cu bolus in experiment 1 had no effect on body weight gains, SC, and sperm normality, progressive motility, and primary and secondary abnormalities; however, treatment in experiment 1 did increase serum Cu concentrations on some but not all days and did not increase concentrations above the normal range for beef cattle. The conclusion made from these experiments is that the sustained Cu boluses used in these studies do not significantly affect growth and reproductive traits in beef bulls with adequate Cu status. / Master of Science