Effects of DHA supplementation of the extender containing egg yolk and α- tocopherol on the freezability and post-thawing fertility of ram semen

• Effects of DHA supplementation of ram semen extenders were evaluated.
• We have investigated freezability and post-thawing fertility of ram semen.
• DHA supplementation of ram semen extenders improved post-thawed semen characteristics.
• Insemination of the DHA enriched extenders resulted in higher fertility rate in ewes after thawing.

The aim of present study was to evaluate the effect of increasing the DHA content of a basic Tris, extender supplemented with different level of fish oil on post-thawing ram semen quality and fertility. The semen samples were collected from four fertile rams, pooled and diluted (1:4) with a Tris–citric acid–fructose–yolk extender, supplemented with different concentrations (0.15, 0.30 or 0.45 g) of fish oil per gram egg yolk. In control group, semen was diluted in the basic diluent, without fish oil. After aspiration into 0.25 mL straws, the semen samples were cooled to 5 °C within 90 min and frozen by exposure to liquid nitrogen vapor. After 24 h, straws were thawed in a water bath (37 °C) for 30 s. All characteristics of frozen-thawed sperms were improved by increasing the level of the fish oil till 0.30 g fish oil (P < 0.01). But, no significant difference was observed between 0.30 and 0.45 g fish oil. The highest values of sperm progressive motility (42.31 ± 1.05), viability (55.70 ± 0.94) and membranes integrity (50.74 ± 0.92) were observed in diluent supplemented with 0.30 g fish oil. The fertility rates obtained following insemination were 18.18%, 47.54% and 45.16%, when using semen cryopreserved in the control, 0.30 and 0.45 g fish oil extenders, respectively. A significant difference was recorded between the control and the DHA added extenders (P < 0.05), but no difference was found between the fish oil contained extenders as such. The results showed that increasing DHA in ram semen extenders can improve seminal quality and its fertility post thawing.