Influence of carbohydrate and supplemental fat source on the metabolizable energy of the diet.

An experiment involving 60 Single Comb White Leghorn laying hens was conducted to measure the influence of the carbohydrate source and supplemental fat on nitrogen-corrected metabolizable energy(MEn) of the diet. Twelve diets with the same calculated metabolizable energy (ME) and protein levels were arranged in a 2 X 6 factorial composed of two different yellow grease to soy oil ratios (6%:0% and 4%:2% of the diet) and 6 corn starch to sucrose ratios (from 49%:0% to 0%:49%). The diets were assayed for MEn content by using the total feces collection method. There was a positive linear relationship between sucrose level and MEn of the diet. When sucrose replaced corn starch, the MEn of the diets increased more than expectd, and these increments were statistically significant (P < .01). The diets containing a mixture of yellow grease and soy oil had significantly higher MEn values than those in which supplemental fat was supplied exclusively as yellow grease (P < .05). A comparison of the "calculated" regression equation describing the expected dietary ME with changing sucrose and soy oil levels, Y = 3110 + 1.03 (% sucrose) + 9 (% soy oil), and the regression equation determined experimentally, Y = 3177 + 3.25 (% sucrose) + 18 (% soy oil), illustrates the relatively large increases in dietary ME caused by sucrose and soy oil. These effects of sucrose and soy oil were independent. These data support the concept that the addition of a relatively unsaturated fat (soy oil) to a saturated fat (yellow grease) enhances dietary MEn. Also, the data indicate that the presence of supplemental fat in the diet increases the utilization of energy from sucrose. Thus, the "extra-caloric" effect of fats on MEn may be the culmination of a favorable interaction between supplemental fats and fats inherent in other diet components, and a beneficial influence of supplemental fats on energy utilization from certain nonlipid dietary constituents.