Sensitivity of pig genotypes to short-term manipulation of plasma fatty acids by feeding linseed

The sensitivity of pigs selected for high daily food intake (DFI), low lean food conversion (LFC) and high lean growth rate (LGS) to dietary change of plasma fatty acids was assessed. The difference between the two diets was effectively a substitution of palmitic (C16:0), oleic (C18:1 n-9) and linoleic (C18:2 n-6) with linolenic (C18:3 n-3) fatty acids. Fatty acid compositions of plasma free fatty acids, neutral lipids and phospholipids were measured in 90 kg animals fed a base or high linolenic (C18:3 n-3) fatty acid diet, based on whole linseed, for four days. There were 24 animals from each selection line and 24 animals from an unselected control line, with boars and gilts represented equally in each line. Half of the selection line animals were fed the base diet and half were fed the high C18:3 diet, but all control animals were fed the base diet. Prior to slaughter, animals were fasted for 18 h. The fatty acids primarily affected by dietary change were C18:3 n-3 and its products, C20:5 n-3 (EPA) and C22:6 n-3 (DHA). The sensitivity of a selection line to dietary change was parameterised by the relative shift in fatty acid composition through changing from the base diet to the high C18:3 diet. In neutral lipids, the sensitivities of C18:3 n-3 in the DFI and LFC lines were similar but greater than in the LGS line (3.0 v. 1.8, S.E.D. 0.15), while, for phospholipid and free fatty acids, the sensitivity of the DFI line was greater than in the LFC and LGS lines (2.3 v. 1.8 and 2.0 v. 1.4, respectively). For C20:5 n-3 and C22:6 n-3, the DFI and LFC lines were more sensitive to dietary change than the LGS line (total lipid : 2.3 v. 1.9 and 1.5 v. 1.2). In general, the DFI line was most sensitive to dietary change and the LGS line was the least sensitive. The difference in sensitivities of the lipid classes to the high C18:3 diet between the selection lines could result from differences in body fat content and may explain the general lack of genotype with nutrition interactions in post-1990 genotypes in comparison with fatter circa-1970 genotypes.