Cod liver oil: feed oil influences on fatty acid composition

The influence of feed oils on fatty acid compositions of cod liver oils was examined to investigate how fatty acid profiles are modified, and to provide estimates of feed oil compositions needed to give liver oils meeting production guidelines [3-11% 18:2n-6, 7-16% 20:5n-3 (EPA) and 6-18% 22:6n-3 (DHA)]. Attention was directed to examination of cod liver oil contents of n-6 and n-3 fatty acids, the essential fatty acids. Data, mostly taken from published work, were subjected to regression analysis to investigate the relationships between the percentages of fatty acids (18:2n-6, total n-6 fatty acids, 18:3n-3, 20:5n-3, 22:6n-3 and total n-3 fatty acids) in feed oils and their percentages in liver oils. There were highly significant relationships between feed oil and liver oil percentages for all fatty acids examined: Liver oil 18:2n-6 (%) = 0.787 Feed oil 18:2n-6 (%) + 1.329; (n = 21; R (2) = 0.957) Liver oil total n-6 Fatty acids (%) = 0.831 Feed oil total n-6 Fatty acids (%) + 0.536; (n = 21; R (2) = 0.957) Liver oil 18:3n-3 (%) = 0.814 Feed oil 18:3n-3 (%) + 0.022; (n = 21; R (2) = 0.985) Liver oil 20:5n-3 (%) = 0.762 Feed oil 20:5n-3 (%) + 1.163; (n = 21; R (2) = 0.875) Liver oil 22:6n-3 (%) = 0.785 Feed oil 22:6n-3 (%) + 1.393; (n = 21; R (2) = 0.831) Liver oil total n-3 Fatty acids (%) = 0.770 Feed oil total n-3 Fatty acids (%) + 2.558; (n = 21; R (2) = 0.851) Feed oil percentages of 18:2n-6, 20:5n-3 (EPA) and 22:6n-3 (DHA) required to produce liver oils that comply with guidelines were estimated to be 2.5-12.5% for 18:2n-6, 8-19.5% for 20:5n-3 and 6-21% for 22:6n-3. Given the fatty acid compositions of commercial feed oils it is unrealistic to expect that liver oils with highly unsaturated n-3 fatty acids percentages at the high end of the recommended range (15-18% for both 20:5n-3 and 22:6:n-6) can be produced from farmed cod, but it should be possible to obtain liver oils that fulfil fatty acid composition criteria without the need to manufacture feeds that have fatty acid compositions that deviate markedly from those in current use. As an alternative to using feeds with constant fatty acid compositions throughout production, finisher feeds could be used to manipulate fatty acid compositions of liver oils, but the economics of using this feeding strategy needs to be examined before commercial implementation can be recommended.