Feeding of fish oil can increase the amount of unsaturated fat present in the tissues, especially of monogastric animals, which can cause the back fat to become soft and off-flavors to develop. The presence of unsaturated fats in the edible portions becomes a more significant problem when those portions are being processed, such as when pork hams are being smoked and cured.
Tissue content of unsaturated fatty acids was found to increase as the level of fish oil in the diet increased in swine (Barowicz et al., 1997). Neonatal piglets are shown to have ample capacity to digest and absorb the lipid components contained in fish oil (Chiang et al., 1989). Fat hardness decreased and iodine number increased of the body tissues of swine when fish oil was fed (Irie et al., 1992). Carcass quality was negatively effected in swine carcasses when fish oil was fed (Urbanczyk et al., 1997). Off-flavors and increased unsaturated fatty acid content in the tissues of swine was observed when 1 to 3 % fish oil was fed (Overland et al., 1996). Feeding 3 to 6 % fish oil to 60 kg pigs was found to cause off-flavors in the edible tissues (Lauridsen et al., 1999).
The unsaturated fatty acid levels in milk from sows fed fish oil increased (Arbuckle et al., 1993). Feeding fish oil to pregnant and lactating swine was found to increase birth weight of piglets, increase piglet weight at 21 days and decrease piglet mortality (Walkiewicz et al., 1993). The progression was retarded and regression of arteriosclerosis was observed when swine was fed fish oil (Sassen et al., 1989). Cholesterol levels associated with the Low Density Lipoprotein were increased when fish oil was fed to sows (Kirchgessner et al., 1994). Feeding of fish oil was found to increase insulin sensitivity in pigs (Behme, 1996).
