Selenium (Se) plays a key role in maintaining integrity of the sperm membrane and modulating quality of ejaculate. A systematic search was conducted based on the following PICO question: "What is the effectiveness of Se supplementation (I) compared to no supplementation (C) on semen quality, testicular circumference and testosterone production (O) in rams (P)". The search was carried out by four experts using the PRISMA framework to avoid bias in the scientific database: PubMed, Google Scholar and Web of Science. The response variables were semen volume (SV), sperm cell concentration (SC), sperm progressive motility (SM), abnormal sperm % (AS), scrotal circumference (Scir), semen pH, serum Se concentration (SSe) and blood testosterone (BT). The effect size was estimated through the standardized (SMD) and raw mean difference (RMD). Heterogeneity was quantified using the I 2 index. The sources of heterogeneity were explored through a meta-regression including the covariates: breed, Se source (organic/inorganic), dosage, latitude, geographical zone, and semen collection technique (artificial vagina/electroejaculator). Oral supplementation of Se depicted a positive effect compared with not supplemented rams to SV (+0.15 ml), SM (+4.74 %), SC (+0.22 %), AS (-1.17 %), Scir (+0.86 cm), SSe (+3.98 µg/ml), and ST (+0.47 ng/ml). SM, AS, SC, and ST outcomes showed a better response to inorganic Se supplementation. There was a positive relationship between latitude and response to Se supplementation in SM and BT. In studies using the electroejaculation technique, the response to Se supplementation in SM and AS was significantly lower (P < 0.05). In addition, the percentage of abnormal sperm was increased with electroejaculation. In conclusion, oral Se supplementation improves semen quality in rams, which could have a positive effect on flock fertility. However, variables such as Se source, dosage and latitude should be considered when supplementing Se orally. • Se supplementation in rams increases sperm volume, motility and concentration while minimizing abnormalities. • Inorganic sources of Se are particularly effective in increasing motility and testosterone levels. • However, factors such as Se source, dosage and geographical location should be considered in supplementation strategies.