The relationship between the dietary provision of α-tocopherol and the concentration of this vitamin in the semen of chicken: effects on lipid composition and susceptibility to peroxidation

This study is an attempt to enhance the resistance of chicken semen to peroxidative damage by supplementing the diet of cockerels with the major lipid-soluble antioxidant alpha-tocopherol. Cockerels at 6 months of age were fed for 8 weeks with feed containing 0, 20, 200 or 1000 mg alpha-tocopherol kg-1. Semen was collected during the final 2 weeks of the supplementation period and the concentrations of alpha-tocopherol in the spermatozoa and the seminal plasma were determined. The concentrations of alpha-tocopherol in whole semen, spermatozoa and seminal plasma were approximately twice as high when the supplementation was 200 mg kg-1 compared with when supplementation was 20 mg kg-1; however, supplementation at 1000 mg kg-1 did not achieve any further increase in these concentrations of alpha-tocopherol. Thus, the concentration of alpha-tocopherol in semen displays only a limited responsiveness to manipulation by dietary means. In contrast, the concentrations of the vitamin in the testes and liver were found to be much more amenable to dietary manipulation, exhibiting increases of six-seven-fold over the whole range of supplementation. However, the dietary-induced increase in the alpha-tocopherol content of semen did result in a significant reduction in the susceptibility of the semen to lipid peroxidation. A further effect of enhancing the concentration of this vitamin in the semen was a significant increase in the proportions of C20-22 polyunsaturated fatty acids in the sperm phospholipids. In addition, the proportion of phosphatidylethanolamine in the phospholipid was increased whereas that of sphingomyelin was reduced at the higher concentrations of alpha-tocopherol supplementation. Thus, an increased dietary intake of alpha-tocopherol does produce beneficial changes in the antioxidant capacity and lipid profile of semen, albeit to a relatively limited extent.