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Phospholipids of avian spermatozoa characteristically contain very high proportions of long-chain (C20–22) highly polyunsaturated fatty acids of the n-6 family and arachidonic (20: 4n-6) and docosatetraenoic (22: 4n-6) acids form the major acyl groups (Darin-Bennett et al., 1974; Ravie and Lake, 1985; Surai et al., 1998a). In contrast, in mammalian spermatozoa, long-chain polyunsaturated fatty acids of the n-3 family, in particular docosahexaenoic acid (22: 6n-3), are predominant (Poulos et al., 1973; Darin-Bennett et al., 1974; Jain and Anand, 1976; Lin et al., 1993; Kelso et al., 1997a). The importance of C22 polyunsaturates in relation to male fertility has been illustrated by studies in humans demonstrating that the amount of 22: 6n-3 in spermatozoa is positively correlated with sperm motility (Nissen and Kreysel, 1983; Zalata et al., 1998; Conquer et al., 1999).

Moreover, the reduction in the number of spermatozoa and in sperm motility in ejaculates from ageing bulls is accompanied by a decrease in the proportion of 22: 6n-3 in sperm phospholipid (Kelso et al., 1997a). In chickens, the decrease in spermatogenesis and semen quality (evident from 60 weeks of age) is accompanied by a decrease in the proportions of both 20: 4n-6 and 22: 4n-6 in the phosphatidylethanolamine fraction of the sperm phospholipids (Kelso et al., 1996). Most notably, the proportion of 22: 4n-6 in total sperm phospholipid showed a significant negative correlation with the age of the chicken but was positively correlated with sperm motility and fertilizing ability