Incorporation of dietary polyunsaturated fatty acids into pork fatty tissues.

The incorporation and elimination rate of dietary PUFA in pork fat was investigated in this study. Experiment 1 examined the incorporation of dietary PUFA into backfat (BF) and into the triglyceride (TG) and phospholipid (PL) fractions of the i.m. fat of the loin. Experiment 2 examined the elimination of PUFA from BF due to withdrawal of PUFA from the diet. In Exp. 1, Piétrain x Seghers Hybrid pigs (70 barrows and 70 gilts averaging 11 wk of age and 30 kg initially) were assigned to five dietary treatments in a 2 x 5 factorial arrangement during a 16-wk feeding period. Pigs received a diet containing about 2.5% tallow (T) for 8, 10, 12, 14, or 16 wk, followed by a diet containing about 15% full-fat soybeans (FFS) for 8, 6, 4, 2, or 0 wk, respectively. Additionally, BF biopsies were taken every 2 wk from eight pigs on the 8-wk FFS dietary treatment, starting from the time pigs were switched to the FFS diet. Linoleic acid [18:2(n-6)], linolenic acid [18:3(n-3)], eicosadienoic acid [20:2(n-6)], arachidonic acid [20:4(n-6)], and PUFA contents in BF increased (P < .01) with time on the FFS diet, but contents of these fatty acids were similar for pigs fed FFS for 6 or 8 wk. The PUFA content of the biopsies rose throughout the FFS treatment; the greatest increase in PUFA occurred during the first 2 wk of feeding FFS. The PUFA content of the TG and PL fractions in i.m. fat of the longissimus muscle tended to increase with time on the FFS diet. The increase was significant (P < .01) in the TG fraction for 18:3(n-3) and in the PL fraction for 20:4(n-6) and 22:6(n-3). In Exp. 2, 11-wk-old pigs (10 barrows and 10 gilts) were fed a FFS-based diet from 11 to 19 wk of age, followed by the T-diet for an additional 8 wk. During the latter period, biopsies were taken every 2 wk. The elimination of PUFA from BF was greatest during the first 2 wk after the dietary change. The PUFA reached the lowest level at the age of 25 wk. These experiments show that the PUFA: saturated fatty acid ratio of BF can be increased from .34, corresponding with a T-based diet, to .55, by feeding a FFS diet for 6 wk before slaughter.