Dietary α-linolenic acid from flaxseed oil or eicosapentaenoic and docosahexaenoic acids from fish oil differentially alter fatty acid composition and characteristics of fresh and frozen-thawed bull semen

Incorporation rates of dietary omega-3 (n-3) fatty acids (FAs) from different sources into bull plasma and sperm and the effects on physiological characteristics of fresh and frozen-thawed semen were determined. Fifteen fertile bulls were assigned to three treatment groups and supplemented for 13weeks with encapsulated fat: (1) SFA-360g/d per bull saturated FA; (2) FLX-450g/d per bull providing 84.2g/d C18:3n-3 (α-linolenic acid) from flaxseed oil; and (3) FO-450g/d per bull providing 8.7g/d C20:5n-3 (eicosapentaenoic acid) and 6.5g/d C22:6n-3 (docosahexaenoic acid, DHA) from fish oil. Blood samples were taken every 2weeks and semen was collected weekly. With respect to the FA supplements, the proportion of α-linolenic acid in plasma increased in the FLX bulls, whereas that of DHA was increased in the FO bulls, within 2weeks. However, changes in the sperm FA fraction were first expressed in the sixth week of supplementation: in the FO and FLX bulls the DHA proportion increased (P<0.001), whereas that of C22:5n-6 FAs (docosapentaenoic acid [DPA] n-6) decreased (P<0.001). Sperm motility and progressive motility in fresh semen were higher (P<0.05), and the fading rate tended to be lower in the FLX than in FO bulls (P<0.06). Furthermore, sperm motility, progressive motility, and velocity in frozen-thawed semen were higher in FLX than in the other groups (P<0.008). These findings indicate that the proportion of DHA in sperm can be increased at the expense of DPAn-6 by either FO or FLX supplementation, indicating de novo elongation and desaturation of short- into longer-chain n-3 FAs in testes. Furthermore, the moderate exchange of DHA and DPAn-6 in the FLX group's sperm was associated with changes in the characteristics of both fresh and frozen-thawed semen, suggesting the importance of the ratio between these two FAs for sperm structure and function.