Incorporation of dietary polyunsaturated fatty acids into pork fatty tissues

The incorporation and elimination rate of dietary PUFA in pork fat was inve stigated 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 eliminati on of PUFA from BF due to withdrawal of PUFA from the diet. In Exp. 1, Piet rain 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 fa ctorial arrangement during a 16-wk feeding period. Pigs received a diet con taining about 2.5% tallow (T) for 8, 10, 12, 14, or 16 wk, followed by a di et containing about 15% full-fat soybeans (FFS) for 8, 6, 4, 2, or 0 wk, re spectively. Additionally, BF biopsies were taken every 2 wk from eight pigs on the 8-wk FFS dietary treatment, starting from the time pigs were switch ed 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 con tents 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 con tent of the biopsies rose throughout the FFS treatment; the greatest increa se 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) i n 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 addition al 8 wk. During the latter period, biopsies were taken every 2 wk. The elim ination of PUFA from BF was greatest during the first 2 wk after the dietar y change. The PUFA reached the lowest level at the age of 25 wk. These expe riments show that the PUFA: saturated fatty acid ratio of BF can be increas ed from .34, corresponding with a T-based diet, to .55, by feeding a FFS di et for 6 wk before slaughter.