Studies on the composition of horse oil. 2. The component fatty acids of lipids from fatty tissues, muscle and liver

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Abstract
The fatty acid composition of the glycerides of the fatty tissues, muscle and liver of the horse as determined by ester fractionation were shown to be generally similar and to contain 25-30% palmitic acid, 3-6% stearic acid, 4-8% hexadecenoic acid, 50-55% C18 unsaturated acids, and minor proportions of myristic, tetradecenoic and C20-22 unsaturated acids. A separate examination of the C18 unsaturated acids showed considerable differences in composition between the different glycerides. The liver glycerides, in particular, contained less oleic acid than the glycerides of the muscle and fatty tissues (33.3-40.4 as compared with 56.3-68.7%) and the ratio C18 triene/diene showed a progressive diminution from 4.22-4.27 to 2.17-2.39 in passing from the glycerides of the fatty tissues to those of the muscle and liver. The liver phospholipins of the horse as compared with the liver glycerides were shown, in conformity with the observations by other workers on a range of different animals, to contain more stearic acid and C20-22 unsaturated acids, but less palmitic and hexadecenoic acid. In addition, the liver phospholipins contained more octadecadienoic acid (26.8-30.1 as compared with 8.4-10%) but less linolenic acid (3.5-4.0 as compared with 20.1-24.8%) than did the liver glycerides. The composition of the C18 unsaturated acids in the muscle phospholipins was found to be similar to that of the liver phospholipins. The distr. pattern of the C18 unsaturated acids together with the nature of the glyceride structure in the fatty depots of pasture-fed horses compared with that of the fats in pasture suggests that the dietary fats of the horse cannot be directly absorbed as such, but that the fatty acids of the diet are mixed in with those synthesized by the animal, and selectively redistributed to form new glycerides.