This study was conducted to determine the influence of a single subcutaneous (SC) injection of melatonin (18 and 36 mg) on testicular hemodynamics, echotexture, plasma testosterone concentration, and sperm quality characteristics during the non-breeding season in Ossimi rams. Eighteen sexually mature, Ossimi rams were randomly allocated into two treated groups that received either 18 mg (Mel 18 group; n = 6) or 36 mg (Mel 36 group; n = 6) of melatonin powder dissolved in 1 ml corn oil (SC) and a control group (n = 6) that received 1 ml corn oil only. Blood collection and ultrasonographic assessment of the testes and supratesticular arteries were conducted immediately before treatment (W0) and once weekly for 8 successive weeks after melatonin injection (W1-W8). Resistive index (RI) and pulsatility index (PI) values were markedly decreased (P ˂ 0.05) within Mel 36 (at W4-W8) and e Mel 18 (at W8) groups, which was not observed within the control group (P ˃ 0.05). Testicular echogenicity was severely reduced (P ˂ 0.05) in Mel 36 (at W4-W5) and Mel 18 (at W8) groups, which was not occurred in the control one (P ˃ 0.05). The concentration of plasma testosterone was increased (P ˂ 0.05) in Mel 36 (at W3-W8) and Mel 18 (at W8) groups, which was not clear for the control rams (P ˃ 0.05). The percentage of progressively motile sperm cells was higher (P ˂ 0.05) in Mel 36 group (at W5-W8), which was not recorded within the Mel 18 or control groups (P ˃ 0.05).The percentages of sperm cells viability and normal morphology were higher (P ˂ 0.05) within Mel 36 (at W6-W8) and Mel 18 (at W7-W8) groups, which was not detected within the control group (P ˃ 0.05).In conclusion, the administration of melatonin ameliorates the testicular function via enhancing the testicular vascular irrigation, testosterone production, and sperm cells’ quality parameters in Ossimi rams. So, we recommend administration of a single SC dose of melatonin (36 mg) at least one month before using rams for breeding especially out of the reproductive season.
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