This study evaluated how adding coenzyme Q10 to the Tris diluent affects semen quality in Holstein bulls after cooling and cryopreservation at 2, 30, 60, and 90 days. Each week, semen was collected from each bull using an artificial vagina and then pooled. The pooled semen was split into three groups: the control group (Q1) received only Tris, while the other two groups had coenzyme Q10 added to the Tris diluent at 0.2 mM (Q2) and 0.5 mM (Q3). The results showed that adding 0.5 mM Co-Q10 significantly increased the total number of progressive motile spermatozoa (×106), the percentage of sperm with normal morphology, plasma membrane integrity, overall sperm function, and acrosome integrity compared with the control groups throughout all experimental periods. In conclusion, the addition of 0.5 mM Co-Q10 improved the post-cryopreservation semen quality of Holstein bulls. This enhancement is expected to increase the fertility rate of artificially inseminated cows and, in turn, support economic growth. Enhanced semen quality will contribute to higher animal productivity, helping to meet growing consumption demands, address the rising population, and adapt to the climate changes currently affecting the planet.