2018) Influences of dietary selenium, zinc and their combination on semen characteristics and testosterone concentration in mature rams during breeding seasonABSTRACT This study was conducted to determine the effect of dietary supplementation of organic zinc (Availa®Zn100) and selenium (Availa®Se1000) on semen characteristics, testes measures and serum testosterone concentration. Twenty Sanjabi rams (50.01 ± 5.6 kg) were randomly divided into four equal groups, given the basal diet as control (C) or supplemented with 0.3 mg/kg Se (SE) or 40 mg/kg Zn (ZN) or 40 mg/kg Zn plus 0.3 mg/kg Se (ZS) for 120 days experiment (from July to November). The semen samples and blood samples were collected every 3 weeks and scrotal circumference was measured every 15 days. The results indicated that scrotal circumference and testosterone concentrations did not differ due to treatment (P > .05). In contrast, semen characteristics were affected by ZS supplementation. The sperm density and total sperm number increased (P < .05) in ZS group. In addition, the progressive sperm motility was higher in ZS (P < .05) than those of SE and C groups. It is concluded that ZS treatment can improve semen characteristics, which may result in overall improvement in reproductive performance of treated Sanjabi rams during the breeding season. ARTICLE HISTORY