A study was made to determine the sequential effects of supplementing of soybean oil and its timing during growing-finishing period upon the fatty acid composition and the depth of porcine subcutaneous fat.
Ten Duroc pigs, each weighing averagely 81.7kg, were allotted into three different dietary groups as follows: (I) four pigs were fed a basal diet (Japanese pig progeny testing ration) as the control diet for 6 weeks. (II) three pigs were fed the basal diet with addition of 5% soybean oil for 4 weeks, followed by feeding of the basal diet for 2 weeks, and (III) three pigs were fed the basal diet for 2 weeks, followed by feeding of the basal diet with addition of 5% soybean oil for 4 weeks.
The porcine subcutaneous fat at loin was biopsied at 2 weeks' interval during the experiment. At the same time, the depth of subcutaneous fat at 1/2 body length and loin were measured by ultrasonography. The biopsied samples were analyzed for fatty acid composition. The results were as described below.
The contents of myristic, palmitic, palmitoleic and stearic acids in the subcutaneous fat hardly varied and were not significantly influenced by either the supplement of oil or its timing. Compared with the pigs in Group I, those of Groups II and III showed increases in the contents of linoleic and linolenic acids in the subcutaneous fat by feeding of diet with oil supplement, whereas the contents of oleic acid were reduced. The changes in the levels of oleic, linoleic and linolenic acids at 2 weeks of feeding of oil-supplemented diet were about half of those at 4 weeks of the feeding. The changes in the contents of three fatty acids seemed to be larger in the Group III than in the Group II. As poly-unsaturated fatty acids were likely to be retained more in the fat, the effect of supplementing of oil to the diet tended to be a little more appreciable during the initial 4 weeks of the experiment than the terminal 4 weeks.
The depth of fat at 4 positions of pigs' bodies gained approx. 1mm in each two weeks of the experiment. The supplementing of 5% oil into diet for 4 weeks tended to increase the depth of fat. The correlation coefficient between the level of linolenic acid and the depth of fat in the subcutaneous fat was significantly high, but tended to decrease by feeding of diet with oil.
These results revealed that the supplementing of 5% of soybean oil to diet for 4 weeks tended to increase the depth of back fat layer of pigs and exert mild influences upon the composition of fatty acids in subcutaneous fat with some variations in it subject to the timing of the supplementing.

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A study was conducted to determine the effects of supplementing of soybean oil into diet and its timing during the growing-finishing period upon the physicochemical characteristics of fat tissues and intramuscular fat in longissimus muscle of pigs.
Ten 4-months old piglets were allotted into three groups of different feeding conditions for 6 weeks. Group I was composed of 4 pigs fed a basal diet as the control. Three pigs each in Groups II and III were given the basal diet with 5% soybean oil during the initial 4 weeks and the terminal 4 weeks, respectively, in the experiment, while the basal diet was fed to them for the balance two weeks. The lipids extracted from the inner and outer layers of back fat, leaf fat and intramuscular fat in longissimus muscle were analyzed by physicochemical methods. The results were as follows. The supplementing of soybean oil into diet increased the contents of linoleic and linolenic acids in lipids but reduced those of oleic acid invariably which were collected from various positions of the bodies of pigs studied. The diet containing soybean oil tended to lower the melting point and the hardness by Texturometer and to raise the iodine number and refractive index of fat in fat tissues of the pigs. From the viewpoint of the level of linoleic acid, the fat in fat tissues appeared to be influenced more appreciably by the oil supplementing than the intramuscular fat. From the viewpoint of changes in the melting point and the contents of saturated fatty acids, the influences of the oil supplementing seemed to be more appreciable in leaf fat than in the inner and the outer layers of back fat. The mean levels of linoleic and linolenic acids and the iodine number in all the fat samples collected from various positions of the pigs' bodies tended to be higher in the Group III than in the Group II. However, the level of stearic acid in fat in the Group III seemed to be slightly higher than that in the Group II, while the contents of saturated fatty acids and the hardness by Texturometer of both groups were almost equal to each other.
Consequently, it was realized that the difference in the timing of oil supplementing by about 2 weeks caused hardly any differences in the firmness of porcine fat, but caused somewhat appreciable influences upon the physicochemical characteristics of the fat.

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