Fatty acid composition of serum lipids in fasting ponies.

Alterations in the fatty acid distribution of total lipid extracts and 4 of the major lipid subclasses of serum in ponies fasted overnight and for 4 and 7 days were determined. Although increases in 16:0, 16:1, and 18:3 omega 3 were observed, decreased amounts of 18:0 and 18:2 omega 6 combined to cause no significant change in the saturated to unsaturated fatty acid ratio in the total extracts. Phospholipid became somewhat preferentially enriched in saturated fatty acids due to a decrease in 18:1, although this response was variable. The free fatty acid and triglyceride fractions both showed increases in relative amounts of 18:3 omega 3 and a decrease in 18:0 and a concomitant change in the saturated to unsaturated fatty acid ratio. This endogenous alteration was most likely due to the mobilization of an increased proportion of polyunsaturated fatty acids from tissue sites with their subsequent incorporation into triglyceride by the liver. It probably reflects the type of forage diet on which the animals had been maintained prior to the study. The fatty acid composition of the cholesteryl ester fractions was unchanged during fasting but contained appreciable amounts of the 18:2 omega 6 fatty acid.