The role of Omega-3 polyunsaturated fatty acids (n-3 PUFAs) on sperm resistance to cooling and storage is controversial. Although previous studies demonstrated that the addition of omega-3 fatty acids to the diet of animals (e.g. pig and horse) can influence sperm membrane fluidity and integrity as well as male fertilizing capacity, there is not enough data about their effects on semen quality in vitro, especially on bovine semen. So, the present experiment was designed to determine the protective effects of various levels of purified n-3 PUFAs on bovine semen quality in vitro in response to cryopreservation. Polyethylene glycol (PEG), as a more suitable solvent has to be added to introduce n-3 PUFAs to semen extenders. Media were finally sonicated. In treatment A, PEG was added alone to the samples and in treatments B, C and D three different concentrations of n-3 PUFAs (1, 2.5 and 5%) in combination with PEG were added to the semen extender (Tris-citrate buffer medium containing egg yolk and glycerol). Five proven bulls were randomly selected; ejaculates were collected by artificial vagina and semen characteristics were recorded. Only ejaculates with normal characteristics (volume > 5 ml; concentration > 1.2 billion/ml; motility > 75%; normal morphology > 85% and viability > 85%) were chosen and diluted semen (40 millions/ml) was loaded into 0.5-mL straws, sealed and frozen. Motility, viability and morphology were investigated in frozen-thawed sperm after 1 month. Motility and other dynamic parameters of sperm were analyzed by computer aided sperm analysis (CASA). The results were evaluated by repeated measure ANOVA using SPSS and p<0.05 was considered significant. Motility were 37.9, 12.8, 13.2, 13.8 and 10.4%; viability were 54.8, 25.7, 27.6, 26 and 19.2%; and normal morphology were 88, 72.7, 80.6, 75.4 and 83.6% for control, treatments A, B, C and D, respectively. Our results showed that PEG has some detrimental effects on sperm motility and viability, whereas the addition of n-3 PUFAs to semen extenders could not attenuate the detrimental effects of PEG and did not significantly (p<0.05) improve bovine sperm quality in vitro. It seems that n-3 PUFAs cannot be effectively introduced to conservation media as well as sperm membrane to modify sperm characteristics. Nonetheless, n-3 PUFAs might rather be supplemented to the diet of bulls in order to modify the fatty acid compositions of sperm and perform their preventive properties.

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