Effect of Feeding Whale Oil on the Depot Fat of the White Rat.

Forty-three female white rats of average weight 154 gm. were fed for 6 weeks on a diet of 62.5% whole wheat flour, 15% casein, 15% skim milk powder, 1.5% precipitated chalk, 1% NaCl, 5% cotton seed oil and 0.3% cod liver oil. Following this control diet, the animals were changed to one containing 10% whale oil and 90% control mixture for 2 weeks, and from then on to a diet of 20% whale oil and 80% control. After 10 weeks of whale oil feeding the control diet was resumed. At intervals during the experiment groups of 6 rats were killed and the depot fat was removed by dissection and rendered. The results of the analysis of the specimens of fat are given in Table I.

From the above data it is concluded that equilibrium between the food fat and the depot fat is established within 4 to 6 weeks on a given diet. The characteristic highly unsaturated fatty acids of whale oil, including acids of the C₁₈, C₂₀ and C₂₂ series with 4, 5 and 6 double bonds, are apparently deposited as such since the bromine content of the polybromides is practically the same as that of the original whale oil. (Chemically whale oil is classed with the fish oils.) A maximum polybromide number of 15.12 containing 67.63% bromine indicates a storage of at least 4.9% of unsaturated acids on a 20% whale oil diet. On the other hand, these acids give a polybromide number only about 1/3 of the theoretical, 1 from which a storage of nearly 15% may be calculated. Resumption of the control diet for 3 weeks still showed a considerable quantity of highly unsaturated acids to be present. When once stored, they are apparently removed only slowly.