The effect of the basal diet on the utilization of fat as a source of true metabolizable energy, lipid, and fatty acids.

An experiment was made to investigate the effect of diet composition on the utilization of beef tallow by adult cockerels. The birds were starved for 24 hr and then force-fed 1 of 3 basal diets (30 g) supplemented with 0, 1.5, 3.0, or 4.5 g of beef tallow. Excreta voided in the subsequent 24 hr was collected. True metabolizable energy (TME) and lipid availability values were measured. The TME value of tallow differed between basal diets and with the level of tallow input. A corn basal permitted greater TME values than a wheat basal but a supplement of soybean lecithins made the wheat basal as effective as the corn basal. Linoleic acid and phospholipid concentrations in the diet appeared to influence tallow utilization. The basic procedures of the TME bioassay permitted measurement of total lipid and fatty acid availability data. Lipid availability paralleled the TME data. Total lipid utilization ranged from 78 to 93% while the utilization of individual fatty acids varied both between acids and within acids between dietary treatments. Unsaturated fatty acids were well utilized (85 to 96%) while saturated acids were less well utilized (57 to 90%), particularly at high levels of input.