Study of effect of adding horsmint ethanol extract and cysteine into extender on fertility features of frozen Baluchi ram semen after thawing

According to an increasing interest for using artificial insemination by sheep producers, finding methods to maintain frozen semen fertility would be important and applicable. One of the freezing semen disadvantages is increasing of free radicals led to enhanced sperm membrane peroxidation then consequently causes lowered semen fertility after thawing. Some plants bearing high levels of plant antioxidants can help to decrease semen peroxidation. Cysteine, in addition, is a precursor of glutathione peroxidase being the most important antioxidant property in semen. Therefore, the aim of the study was to investigate the effect of adding different levels of ethanol extract of Mentha Longifolia (0, 100 and 200 microL/ml) and cysteine (0, 5 and 10 mmol/l) into ram semen on fertility features after freezing and thawing processes.

In the study, semen samples were collected from four mature, fertile Baluchi rams (> 2y-old) by artificial vagina and after initial evaluation were pooled together. Then, samples were extended in an extender based on Tris-egg yolk. Treatments were arranged as a 3×3 factorial experiment including nine treatments and six straws were assigned to each as replicate. After treating, the straws were filled by the equal amount of semen and after chilling in refrigerator (4 °C) for two hours were frozen in liquid nitrogen container. After thawing the straws at day 10, sperm motility parameters were assayed by CASA. Furthermore, the percentages of viability, plasma membrane integrity and normal morphology of sperms were evaluated by microscope. Data were analyzed by SAS software using GLM procedure and the means comparison was performed by Tukey-Kramer test at 5% error.

Results of the study showed that the effects of adding horsemint extract and cysteine into the extender and the interaction between them on the all motility and viability parameters of frozen ram sperm after thawing were significant (p<0.05), exempt for sperm morphology where only the effect of adding cysteine was significant. Means comparison showed that the greatest sperm total motility, plasma membrane integrity, linearity and curvilinear velocity were observed in cysteine10 treatment (without horsemint extract), while the greatest sperm viability, straight line velocity and average path velocity were seen in cysteine5 treatment (without horsemint extract). The greatest sperm progressive motility percentage was observed in horsemint200 group (without cysteine).

In general, considering to the beneficial effect of adding cysteine into the extender based on tris- egg yolk on the most of fertility parameters of ram frozen semen after thawing, using levels of 5 and 10 mmol cysteine per ml extender in order to maintain fertility of frozen ram semen is recommended.