Injectable trace-mineral supplementation improves sperm motility and morphology of young beef bulls1

This experiment evaluated effects of supplemental s.c. trace-mineral injections on growth and breeding soundness of bull calves. Weaned bulls (n = 488; initial BW = 308 ± 45 kg, initial age = 203 ± 17 d) of 2 breeds (Angus and Charolais) and originating from 13 ranches in the Great Plains were transported to a common confinement facility and assigned randomly to 2 treatments: (1) s.c. injections of trace mineral (TM) containing 15 mg/mL Cu, 5 mg/mL Se, 10 mg/mL Mn, and 60 mg/mL Zn or (2) s.c. injections of physiological saline (control). Treatments were administered at arrival (d −2 or −1; 1 mL per 45 kg of BW) and on d 90 ± 1 (1 mL per 68 kg of BW). On d 0, bulls were stratified by treatment, breed, and ranch of origin and assigned randomly to 8 pens in which they were fed a growing diet for 225 d. The diet was formulated to promote a 1.5-kg ADG at a DMI of 2.6% of BW and to meet or exceed NRC (2000) requirements for Ca, Co, Cu, I, Mg, Mn, Na, P, K, Se, and Zn. Initial BW were measured and pretreatment blood plasma samples were collected on d −2 or −1. Breeding soundness examinations (BSE) were conducted and BW were measured at 10 and 12 mo of age (d 90 ± 1 and d 150 ± 1, respectively). Scrotal circumference was measured and semen samples were collected via electro-ejaculation. Motility and morphology of sperm were evaluated via light microscopy. Scrotal circumference, BW, and ADG did not differ (P ≥ 0.16) between treatments at any time. Proportions of control- and TM-treated bulls achieving minimal satisfactory BSE classifications did not differ at 10 mo of age (P = 0.98; 50 ± 3.8% for both TM and control) or at 12 mo of age (P = 0.43; 89 and 86 ± 2.2% for TM and control, respectively). Conversely, improved (P = 0.05) sperm motility was detected in TM-treated bulls compared with control-treated bulls at 12 mo of age; moreover, TM-treated bulls had greater (P ≤ 0.05) improvements in sperm morphology and motility between 10 and 12 mo of age than control-treated bulls. Among bulls that failed BSE at 10 mo of age, more TM-treated bulls tended (P = 0.10) to pass BSE at 12 mo of age than control-treated bulls (98 and 94 ± 1.6% for TM and control, respectively). Under the conditions of this experiment, sperm motility and morphology at 12 mo of age were improved in bulls treated with injectable TM at 7 and 10 mo of age compared with bulls treated with saline.