To measure the effects of dietary n - 3 polyunsaturated fatty acid (PUFA) supplementation on the reproductive capacity of adult male turkeys in industrial flocks, the males of 22 commercial farms were fed either a standard diet or a fish oil diet enriched in n - 3 PUFAs. The fatty acid composition of the spermatozoa and reproductive performance were measured throughout the reproductive period. The fish oil diet very effectively increased the percentage of n - 3 fatty acids (FA) (22:5n - 3 and 22:6n - 3) in spermatozoa and correspondingly decreased the percentage of n - 6 PUFAs (20:4 - 6 and 22:4n - 6): the n - 3/n - 6 ratio in spermatozoa fatty acids were 0.04-0.07 with the standard diet and 0.32-0.4 with the fish oil diet. These changes did not affect the spermatozoa content of n - 9 PUFAs, particularly of 22:3n - 9 which is abundant in turkey spermatozoa (9-12% of the total fatty acids). The supplementation was effective in the middle as at the end of the reproductive period. The reproductive capacity of males was modified by the diet and the positive effect of the n - 3 supplemented diet increased with age (increase in hatching rates of nearly 2 points at 48-58 weeks for males fed fish oil diet). These results indicate that an increase in the dietary ratio of 11 - 3/n - 6 PUFAs is valuable to sustain the reproductive capacity of male turkeys especially when they are getting older.