A slope-ratio precision-fed rooster assay for determination of relative metabolizable energy values for fats and oils.

The precision-fed rooster assay (PFRA) frequently yields TMEn values for fats and oils in excess of their gross energies. Six experiments were conducted to determine if the PFRA could be combined with a slope-ratio type assay to yield more useful lipid TMEn values. In experiment (EXP) 1, refined corn oil (RCO) was fed to conventional and cecectomized roosters at zero, 5, 10, 15, and 20% of a ground corn diet. In EXP 2 through 6, lipids were fed to conventional roosters at zero, 5, and 10% in a ground corn diet. Palomys (a novel lipid), high stearidonic acid soybean oil (SDASO), 2 animal-vegetable blends (AV1, AV2), a vegetable-based oil blend (VB), and corn oil from an ethanol plant (DDGSCO) were evaluated and compared to refined soybean oil (RSO) or RCO as the reference lipid. Multiple linear regression of diet TMEn on supplemental lipid level generated regression coefficients that were used to calculate relative bioavailability values (RBV). In EXP 1, RCO was a suitable reference material as TMEn linearly increased up to 20% RCO inclusion. There were some minor differences in TMEn of RCO between conventional and cecetomized bird types. In EXP 2, Palomys was found to have a lower (P < 0.05) RBV (87%) than RCO. In EXP 3, there were no significant differences between SDASO and RSO. In EXP 4, the RBV of AV2 (79%) was lower (P < 0.05) than RCO, while the RBV of AV1 was not different from RCO. The RBV of DDGSCO (116%) was higher (P < 0.05) than RCO in EXP 5. The RBV of VB (84%) was lower (P < 0.001) than RCO in EXP 6; however, this may be an underestimation for low levels of VB, as there was an interaction (P < 0.01) between lipid type and lipid supplementation level. These results indicate that the precision-fed slope-ratio rooster assay can detect differences among lipids and yields practically useful lipid TMEn values.