The Effect of the Basal Diet on the True Metabolizable Energy Value of Fat

An experiment was made to measure the effect of the basal diet on the true metabolizable energy (TME) value of beef tallow. Sixteen diets were arranged as a 4 × 4 factorial with four basal diets (wheat and soybean; corn and soybean; wheat, soybean and meat; wheat, soybean and fish) and four levels of added tallow (0, 5, 10, 15%). Each diet was assayed for TME 8 times and the TME value of the tallow was calculated by difference. Chloroform: methanol extracts of the basal diets were fractionated into neutral and phospholipids. The fatty acid compositions of total, neutral and phospholipid fractions were determined. The tallow supplemented diets were assayed for fatty acids. The TME value of the tallow decreased with the level of dietary inclusion (P<0.01) and also differed according to the basal diet with which it was fed. The corn: soy basal gave higher TME values for the tallow than did the other three basals. There was no significant interaction between the basal diets and the level of fat inclusion. There were significant linear relationships between the TME value of the tallow and the amounts of phospholipid and linoleic acid per unit weight of dietary fat.