Effects of melatonin and a photoperiod regimen on semen characteristics and hormonal status of Afshari rams out of breeding season

It is well known that rams show a marked seasonal variation in many reproductive aspects, including testicular size, semen production, plasma testosterone concentration and sexual behavior –characteristics that generally increase from spring to autumn. These changes are mainly regulated by photoperiod with long days being inhibitory and short days being stimulatory. The administration of melatonin at the appropriate time of the year, or following a treatment of long days can mimic the stimulatory effect of natural short days in advancing the period of maximum reproductive activity in the ram. The objective of this study was, therefore, to determine whether treating rams with melatonin and photoperiod in mid-spring increased testicular and semen concentration parameters. The aim of present study was to investigate the effects of melatonin and changes in photoperiod regimen on semen characteristics of Afshari rams out of the breeding season.

Twelve rams were randomly allocated into three groups: In control group rams were exposed to natural day photoperiod. In Melatonin group rams were treated as the same as control group plus two 18 mg of melatonin implants one in the area under the skin of the left ear and another in the area below the right ear. In photoperiod regimen group rams were managed as the same as group 1 and 2 until 4 pm (8 hours light) and thereafter were kept in dark stall until 8 am. Plasma melatonin and testosterone concentrations were measured by commercial kits. Testicle dimensions were measured five times during experiment and semen samples were taken 2 days a week for 8 weeks.The data were analyzed in a randomized complete block design.

The results showed that photoperiod regimen increased semen wave motion motility in compare to control group (P= 0.01). In addition, sperm concentration in melatonin treatment group (5.32±0.25) significantly increased in compare to control group (4.12±0.25) and photoperiod regimen group (4.15±0.25) (P=0.002). Plasma melatonin concentration in melatonin treatment group increased in compare to photoperiod regimen group and control group on different sampling days (P= 0.05). Plasma testosterone concentration was not affected significantly in experimental groups on different sampling days following melatonin or photoperiod treatments (P= 0.05).

In general, melatonin implants increased sperm concentration, and Photoperiod increased Progressive velocity of Afshari rams, but did not effect on other sperm parameters. melatonin implants increased plasma melatonin concentration but photoperiod did not effect on plasma melatonin concentration.