In our previous study we have examined the incorporation of various dietary omega-3 (n-3) fatty acids (FA) into bull sperm and the effects on physiological parameters of fresh and frozen-thawed sperm. We have found a moderate exchange of C22:6n-3 (DHA) and C22:5n-6 FA (DPAn-6) in the sperm of bulls fed flaxseed than fish oil, which improved the survival, motility, progressive motility and velocity of frozen-thawed sperm. In the present study we have compared the effects of a different dietary supplementation of C18:3n-3 (ALA) on the incorporation into sperm, and conception rates of cows inseminated with semen from both groups. Ten fertile bulls from the “SION inseminating bulls” list were divided into 2 groups according to age and physiological parameters of semen collected during the month prior to the study. The bulls were fed either a control diet or provided with a supplement contained 30% fat from flaxseed oil. The treatment bulls (FLX) were supplemented daily with 215 g/d of ALA. Semen was collected every 2 wks for FA analysis. Data were analyzed using the PROC MIXED procedure of SAS. The concentration of ALA was negligible in both groups. The proportion of C22:5n-6 (DPA-n6) was lower, while the proportion of C22:6n-3 (DHA) was higher in sperm of the FLX than control bulls (8.6 and 18.8%, and 26.5 and 17.7%, respectively; P<0.001). Moreover, the proportion of total polyunsaturated fatty acid (PUFA) or other FAs families did not change in sperm of FLX bulls, but an exchange between DPAn-6 and DHA was evident. The results indicate on desaturation and elongation capacity of the testes tissues, in which dietary ALA was converted to the longer PUFA – DHA. Cows are being inseminated with semen from both groups, and conception rates of the cows will be analyzed.