The fatty acid profiles of yolk lipids vary greatly among avian species in the wild. This results partly from the major differences in the pattern of polyunsaturated fatty acids (PUFAs) provided by different dietary modes. For example, granivorous species that obtain linoleic acid (18:2ω-6) from dietary seed oils incorporate high proportions of 18:2ω-6 into their yolk lipids. By contrast, yolks of herbivorous birds are rich in α-linolenic acid (18:3ω-3), derived from the lipids of grasses and leaves. Arachidonic acid (20:4ω-6) is the characteristic yolk PUFA of carnivorous birds, because this fatty acid is well represented in the tissue lipids of their prey. Typically, docosahexaenoic acid (22:6ω-3) and other ω-3 HUFA derived from fish lipids predominate in the yolks of piscivorous birds. Yolk fatty acid composition is also influenced by genetic factors relating to aspects of maternal metabolism that determine the selective incorporation of particular PUFAs into the yolk. Ultimately, the yolk fatty acid profile results from the interplay between diet and phylogeny. The effects of phylogeny are illustrated by, for example, the similar fatty acid compositions of the yolks of several species of ducks with different dietary preferences. Most species of birds in the wild lay eggs that have ω-6:ω-3 ratios close to unity. This contrasts with eggs of the domestic chicken where this ratio is greater than 10:1. The fatty acid profiles of eggs laid by pheasants, geese, ostriches, partridges, ducks, and kestrels in captivity are markedly different from those of the same species in the wild. In particular, the yolks of the captive birds are relatively deficient in 18:3ω-3, 22:6ω-3 or both, and have much higher ω-6:ω-3 ratios, in comparison with the values for the yolks of their free-living counterparts. Considering all avian species for which data is available, the mean yolk ω-6:ω-3 ratio in the wild = 1.52 ±0.99 (mean ±SD; n = 23 species). The mean value of this ratio for species in captivity = 15.8 ±9.5 (n = 9 species). On average, therefore, the yolk ω-6:ω-3 ratio is some 10 times greater in captivity than in the wild. In this light, the fortification of table eggs with ω-3 PUFAs to enhance human health can simply be seen as a return to the natural situation.
|Title of host publication||Wild-Type Food in Health Promotion and Disease Prevention|
|Subtitle of host publication||The Columbus Concept|
|Number of pages||17|
|Publication status||Print publication - 1 Dec 2008|
- and ω-3 PUFAs
- Fatty acids
- wild birds