Retention of n-3 polyunsaturated fatty acids in trimmed loin and belly is independent of timing of feeding ground flaxseed to growing-finishing female pigs1

A serial slaughter study, involving 45 individually housed Yorkshire female pigs, was conducted to evaluate the impact of feeding diets containing ground flaxseed (FS) during either the grower or late finisher phase on the incorporation of α-linolenic acid (18:3n-3) and n-3 highly unsaturated fatty acid metabolites (n-3 HUFA; all n-3 PUFA excluding 18:3n-3) in trimmed loin (longissimus dorsi) and belly (cross-section cut). Growth performance, carcass characteristics, and pork quality were also monitored. The three feeding regimens were 1) feeding a diet containing 10% FS between 25 and 50 kg BW, followed by FS-free diets (low n-3 PUFA content) until 110 kg BW (FS early, FSE; n = 16), 2) feeding no FS diets between 25 and 85 kg BW, followed by a diet containing 6% FS until 110 kg BW (FS late, FSL; n = 17), and 3) feeding FS-free diets between 25 and 110 kg BW (CON; n = 8). Pigs were assigned to 1 of 3 target slaughter weights for determining whole nutrient retention: 50 kg (n = 4 and 5 for FSE and FSL, respectively), 85 kg (n = 4 for FSE and FSL), and 110 kg (n = 8 pigs for FSE, FSL, and CON). An additional 4 pigs were slaughtered to determine initial body composition at 25 kg BW. Pigs on treatments FSE and FSL consumed equal cumulative amounts of FS (5.1 vs. 5.2 kg). Fatty acid content was expressed as milligrams per 100 g of fresh tissue. No treatment effect was observed for growth performance, body composition, carcass characteristics, loin meat quality, and fat content in the loin and belly samples. In the loin, the content of 18:3n-3 at 110 kg BW was greater for FSL than FSE and CON (P < 0.01; 143, 76.4, and 37 mg/100 g, respectively), whereas the contents of 18:3n-3 in the belly were greater for both FSL and FSE than CON (752, 667, and 207 mg/100 g for FSL, FSE, and CON, respectively). Within tissues, the content of n-3 HUFA was similar for FSL and FSE, and both were greater (P < 0.01) than CON for loin (41.7, 30.3, and 17.9 mg/100 g, respectively) and belly (168, 179, and 71.2 mg/100 g, respectively), except for docosahexaenoic acid (22:6n-3) in the loin. Feeding FS tended to reduce the content of arachidonic acid (20:4n-6) and adrenic acid (22:4n-6; P < 0.10) in the loin and belly. In the belly but not in the loin, feeding FS reduced the content of total SFA (P = 0.05) and tended to reduce the content of the sum of MUFA (P = 0.09). Within the loin and belly, the ratio of n-6 to n-3 PUFA and the content of n-3 HUFA were similar for FSE and FSL, with the exception of 18:3n-3 and 20:4n-6 in the loin, for which contents were greater for FSL than FSE (P < 0.05). These results indicate that providing modest amounts of FS leads to a substantial enrichment of 18:3n-3 and n-3 HUFA in pork products. The enrichment of n-3 HUFA appears to be independent of timing of feeding FS, providing flexibility as to when n-3 PUFA can be fed to generate n-3 PUFA-enriched pork products.