Lipid manipulation of chicken semen by dietary means and its relation to fertility : a review

The major polyunsaturate in phospholipids of chicken spermatozoa is docosatetraenoic acid, 22:4n-6, which is positively correlatable with sperm motility and fertility. The potential for dietary manipulation of sperm fatty acid in order to improve male fertility has been extensively studied in the chicken. The effects of diets enriched in n-3 and n-6 long chain polyunsaturates have been investigated in different trials using different oil sources and levels of oil inclusion. The 22:6n-3 and 22:5n-3 content of avian spermatozoa is increased by supplementing the feed with fish oil (rich in 22:6n-3) and linseed oil (rich in 18:3n-3) respectively. The 22:4n-6 content is also increased by supplementing the feed with evening primrose oil (rich in 18:3n-6) in association with high level of vitamin E (200 mg/kg) and with arasco oil (rich in 20:4n-6). The effects of these fatty acid manipulations on sperm quality and/or fertility are reviewed. Both n-3 and n-6 rich diets showed a positive effect on sperm movement during the reproductive period and an age-dependent positive effect on fertility. Reported effects of n-6 rich diets on semen production have been variable with 20:4n-6 rich diet having a positive effect on semen volume and thus on total sperm number and 18:3n-6 rich diets having a negative effect on semen concentration. Spermatozoa enriched in 22:5n-3, or 22:6n-3 or 22:4n-6 result in significantly higher fertility values following artificial insemination compared to control spermatozoa; however, such a positive effect is age dependent and observed at 37 to 42 weeks, but not in older birds. The n-6 fatty acid composition of chicken spermatozoa is recognised as a specie-specific characteristic. The fundamental relation between dietary lipid, spermatozoa fatty acid composition and thus sperm quality and fertility can be seen as having a potential commercial application.