Effects of supplementation of the Tris-egg yolk extender with n-3 polyunsaturated fatty acids (PUFAs) on frozen-thawed ram semen characteristics

The present study was conducted to evaluate the effects of supplementation of Tris-egg yolk extender with the different concentrations of n-3 PUFAs (DHA + EPA) on the freezability of ram semen. Semen samples were collected from five fertile rams using an artificial vagina, once a week, for 8 weeks in July and September. The selected ejaculates were extended and pooled into Tris-egg yolk extender supplemented with 0 (control), 10, 30 and 50 ng ml−1 concentrations of n-3 PUFAs. The extended samples were cooled for 3 h at 4 °C and packed in 0.5 ml straws, frozen in liquid nitrogen for a week. The mean percentage of sperm motility in 50 ng ml−1 (35.6 ± 1.8%) and 30 ng ml−1 (37.5 ± 1.8%) n-3 FAs supplemented groups was significantly lower than that of control group (43.1 ± 1.8%; P < 0.01). The mean percentage of sperm viability in 30 ng ml−1 (38.9 ± 1.5%) and 50 ng ml−1 (36.4 ± 1.5%) n-3 FAs supplemented groups was significantly lower than that of control group (43.8 ± 1.5%; P < 0.01). The plasma membrane integrity was significantly lower in 50 ng ml−1 n-3 FAs supplemented group (29.6 ± 1.6%) than that of control group (34.2 ± 1.6%; P < 0.05). The mean percentage of sperm tail defects was also significantly higher in group containing the n-3 FAs of 50 ng ml−1 (P < 0.05). In addition, post-thaw sperm motility (P < 0.05), viability (P < 0.001) and plasma membrane integrity (P < 0.05) in n-3 FAs supplemented groups decreased more significantly in September than those in July. In conclusion, the addition of n-3 PUFAs in Tris-egg yolk extender did not improve the freezability of ram semen and had more detrimental effects on sperm cell after freezing-thawing in the breeding season.