The amount of oil in the diet and its degree of unsaturation are known to exert an important effect on the nature of the fat deposited in the body of the growing pig, foods of high oil content tending to give rise to bacon carcasses containing fat of an undesirably soft and unsaturated character. For this reason, authorities on pig nutrition are agreed on the desirability of excluding from the dietary of the bacon pig all foods containing more than a small percentage of oil. It has been stated that, in order to avoid the danger of producing carcasses with soft fat, the meal ration of the fattening pig should be made up so as to contain no more than about 3% of oil.

This prejudice against the use of feeding stuffs rich in oil has been transferred, somewhat unquestioningly perhaps, to feeding stuffs rich in fat. Feeding meat meal, for example, contains normally from 8 to 10 % of fat, and manufacturers complain of the difficulty of securing sales of this product for pig-feeding on account of the view generally held that its high fat content would occasion the production of soft fat in the resultant bacon or a carcass with an excessive amount of fat. To meet this prejudice, therefore, the meat meal as ordinarily produced is frequently submitted to a process of de-greasing with petroleum benzine at about 200° F. so as to give a meat meal containing about 3% of fat. This procedure, however, not only adds to the cost of the manufacture of meat meal, but may actually lead to a distinct lowering of the digestibility of the product (Woodman & Evans, 1937).