Abstract
This investigation aimed to study the effects of varying light exposure durations on ram sperm. A total of 25 rams were randomly divided into five groups. The control group was exposed to light durations of 12 h, while the experimental groups were exposed to light durations of 14, 16, 18, and 20 h. After three months of rearing, semen was collected from each ram four times using the artificial vagina method. The sperm motility parameters, sperm abnormality, sperm concentration, acrosome integrity, membrane integrity, semen volume, and total sperm number were measured. Thereafter, the metabolome, amino acid level, testosterone content, plasma follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, and sperm antioxidant capacity were measured. The results showed that the sperm motility, sperm concentration, ejaculation volume, total sperm number, acrosome integrity, and membrane integrity in the 16 h light group were significantly improved compared to the control (p < 0.05), meanwhile the sperm abnormality was decreased. Moreover, we found 345 different metabolites between the control and 16 h light group. Among these, 273 were upregulated and 72 were downregulated. Furthermore, the amino acid content of the seminal plasma in the 16 h light group was significantly increased (p < 0.05) compared to the control. Interestingly, the seminal plasma testosterone content and the levels of FSH and LH in the serum in the 16 h light group were significantly increased (p < 0.05) compared to the control. In terms of the sperm antioxidant capacity, it was observed that the CAT activity was the highest in the group exposed to 16 h of light and decreased at 18 h of light exposure when compared to the control group; however, the CAT activity at 20 h was not different from the control. Additionally, within the 14 to 18 h light exposure range, prolonged light exposure increased the GSH content (p < 0.05), whereas 20 h of light exposure reduced the GSH content. The MDA levels decreased with prolonged light exposure, reaching the lowest point at 16 h (p < 0.05), but increased again at 20 h of light exposure. KEGG analysis indicated that the differential metabolites were mainly involved in metabolic and synthetic activities. Based on the results of this study, we can conclude that the artificial extension of the light duration for 16 h has a positive effect on ram sperm quality.