THE RELATIONSHIP BETWEEN THE DIETARY PROVISION OF ALPHA-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 m ajor lipid-soluble antioxidant alpha-tocopherol. Cockerels at 6 months of age were fed for 8 weeks with feed containing 0, 20, 200 or 1000 m g alpha-tocopherol kg(-1). Semen was collected during the final 2 week s of the supplementation period and the concentrations of alpha-tocoph erol in the spermatozoa and the seminal plasma were determined. The co ncentrations of alpha-tocopherol in whole semen, spermatozoa and semin al plasma were approximately twice as high when the supplementation wa s 200 mg kg(-1) compared with when supplementation was 20 mg kg(-1); h owever, supplementation at 1000 mg kg(-1) did not achieve any further increase in these concentrations of alpha-tocopherol. Thus, the concen tration of alpha-tocopherol in semen displays only a limited responsiv eness to manipulation by dietary means. In contrast, the concentration s of the vitamin in the testes and liver were found to be much more am enable 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 sig nificant reduction in the susceptibility of the semen to lipid peroxid ation. 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, t he proportion of phosphatidylethanolamine in the phospholipid was incr eased whereas that of sphingomyelin was reduced at the higher concentr ations of alpha-tocopherol supplementation. Thus, an increased dietary intake of alpha-tocopherol does produce beneficial changes in the ant ioxidant capacity and lipid profile of semen, albeit to a relatively l imited extent.