The effects of including triglycerides with arachidonic [20:4(n-6)] or docosahexaenoic acid [22:6(n-3)] in formula on plasma chylomicron, LDL and HDL, liver, heart, kidney and brain (n-6) and (n-3) fatty acids were investigated in formula-fed piglets. Piglets were fed formula with (in % total fatty acids) 20% 18:2(n-6) and 2% 18:3(n-3) without or with 0.8% 20:4(n-6) or 0.3% 22:6(n-3) from birth to 18 d. The effects of adding 20:4(n-6) or 22:6(n-3) to the formula differed among different tissues and lipids, with the brain showing resistance to change, Piglets fed formula with 20:4(n-6) had significantly higher plasma, heart and kidney phospholipid and triglyceride, and liver triglyceride 20:4(n-6), but lower plasma and tissue phospholipid 18:2(n-6) than piglets fed formula without 20:4(n-6). Supplementation with 22:6(n-3), in contrast, had no effect on plasma or tissue 18:2(n-6). Higher 22:6(n-3) in liver phospholipid (30-92% greater) and triglyceride (200% greater) in piglets fed formula with 22:6(n-3) rather than without 22:6(n-3) was accompanied by lower 20:4(n-6) in liver phosphatidylethanolamine (mean +/- SEM, 8.6 +/- 0.4 and 10.5 +/- 0.4% fatty acids, respectively), but higher 20:4(n-6) in triglyceride (5.2 +/- 0.4 and 11.5 +/- 0.5%, respectively), and higher liver, heart and kidney phospholipid 20:5(n-3). These results indicate competitive interaction between dietary 20:4(n-6) and tissue 18:2(n-6), and between dietary 20:4(n-6) and tissue 20:5(n-3), rather than 22:6(n-3). The results also show that even at low intakes, dietary 22:6(n-3) or 20:4(n-6) supplementation alters the tissue phospholipid 20:4(n-6) to 20:5(n-3) balance. Studies on the physiologic effects of dietary 20:4(n-6) and 22:6(n-3) supplementation should consider the different sensitivity among tissues to dietary fatty acids.
