Experiments were conducted to assess the effect of feeding diets containing ground flaxseed (FS); as a source of α-linolenic acid (18:3n-3), on whole body retention efficiency (RE) and disappearance (indirect measure of oxidation) of 18:3n-3, and apparent conversion (AC) of 18:3n-3 to n-3 highly unsaturated fatty acids (HUFA) in growing female pigs, using the mass balance approach (serial slaughter). Oxidation of 18:3n-3 was determined directly based on feeding U-13C-18:3n-3 and appearance of 13C in expired breath. Growth performance, composition of growth, body composition, and carcass and loin meat characteristics were not affected by feeding FS containing diets (P > 0.10). In selective pork cuts and the whole body, feeding FS increased (P < 0.10) the contents of 18:3n-3, eicosatrienoic acid (20:3n-3), eicosapentaenoic acid (20:5n-3), and docosapentaenoic acid (22:5n-3) but not docosahexaenoic acid (22:6n-3; P > 0.10). Expressed as a proportion of intake, RE of 18:3n-3 declined with duration of feeding FS (d 0 to 15 vs. d 15 to 30; P = 0.098; 68.4 vs. 52.8%). Similarly, the AC of 18:3n-3 to 20:3n-3 (8.87 vs. 5.53%) and 22:6n-3 (1.27 vs. 0.54%) was reduced over time (P < 0.05), whereas disappearance of 18:3n-3 increased over time (P = 0.074; 2.12 vs. 23.7%). At similar cumulative intake of 18:3n-3, stage of growth (25 to 50 vs. 85 to 110 kg BW) did not impact (P > 0.10) RE of 18:3n-3 and the sum of all n-3 polyunsaturated (PUFA; 95 vs. 110%), AC of 18:3n-3 to n-3 HUFA (19 vs. 22%), and oxidation of 18:3n-3 (7.0 vs. 5.6%); these parameters were influenced by dietary 18:3n-3 level. Pigs fed low dietary 18:3n-3 (0.8 g/kg) yielded both higher RE and AC of 18:3n-3 to n-3 HUFA than pigs on high dietary 18:3n-3 intake (15 g/kg). Oxidation of 18:3n-3 tended to increase with dietary 18:3n-3 level (P = 0.077; 7.97 vs. 4.67% for pigs on high and low dietary 18:3n-3, respectively) and was not affected by previous 18:3n-3 intake (P > 0.10). Feeding modest amounts of FS leads to a substantial and predictable enrichment of n-3 PUFA in pork without compromising carcass and meat quality. The content of n-3 PUFA appears to be independent of timing of feeding n-3 PUFA, providing flexibility as to when n-3 PUFA can be fed for generating n-3 PUFA enriched, value added pork.