Metabolizable Energy Values of Fats Measured by Several Procedures

Abstract

Six experiments were conducted to measure the available energy values of 11 feed fats by several procedures. The apparent metabolizable energy (AME) values of two fats were measured with turkey poults using the total collection and fiber ratio procedures. The fats differed in energy content but there were no significant differences attributable to methodology. When feed conversion data were used to calculate adjusted AME values, the resultant means did not differ from those obtained directly. The second experiment involved the measurement of the AME values of four fats using male broiler chicks. While the fats differed in AME content, the data obtained by the total collection technqiue were similar to those obtained using the fiber ratio procedure. In the third experiment, chicks of two ages were used to assay three fats using the total collection assay and the adjusted metabolizable energy technique. In Experiment 4, male and female poults of two ages were used to assay two fats using the total collection procedure. There were no differences attributable to either age or sex. Experiment 5 was an assay for true metabolizable energy (TME) using adult Single Comb White Leghorn roosters. The four fats previously assayed in Experiment 2 were evaluated at four levels of dietary inclusion (0, 5, 10, 15%). The level of inclusion had a variable effect upon the TME values of the fats. In the final experiment, the TME values of the seven fats used in Experiment 1, 3, and 4 were measured with adult roosters.Comparisons among the various energy values lead to several conclusions. The crude fiber ratio technique yields data similar to that obtained by total collection. Only 45% of the variation in TME values was associated with the variation in the corresponding AME values. This may be explained in part by the use of birds of differing species, sexes, and ages in the AME assays. Both AME and TME values tended to increase with the iodine values and linoleic acid levels of the fats, but such relationships can be misleading.