Comparison of Two Direct Bioassays Using Adult Cocks and Four Indirect Methods for Estimating the Metabolizable Energy-Content of Different Feedingstuffs ,

Abstract

Ninety-six adult Single Comb White Leghorn males were divided into two 48-bird groups to assay feedingstuffs for apparent metabolizable energy (AME) and true metabolizable energy (TME). The metabolizable energy contents of corn, wheat, oats, rye, barley, glucose and soybean, rapeseed, sunflower, dehydrated alfalfa, feather, and fish and meat meals were evaluated. The experiment consisted of three replicates in a cross-over design. The excreta voided by birds in both assays was collected quantitatively at 24- and 48-hr intervals after feeding. A set of corrected AME values (AMEC) was obtained by correcting AME results for endogenous excreta losses. A prediction of AME results was also obtained by using the chemical composition of the 13 feedingstuffs.Birds trained for the AME assay to eat their feed requirements in 1 hr consumed less than ad libitum fed birds even after 14 days of training. Introduction of experimental diets caused a further reduction in intake even though all feeds were pelleted and of similar color. Thirty-nine of 117 AME values were discarded because intakes were less than 50 g/bird. Two TME values were discarded due to problems unrelated to feed. The AME values for the feedingstuffs tested were different (P<.05) from the AMEC and TME results; the latter were not different (P>.05) from each other. Differences (P>.05) in the AME, AMEC, and TME values between the 24-and 48-hr excreta collections indicated that there were differences in clearance rates of feed residues. When AME values were predicted from chemical composition, the error of prediction ranged from .28 to .40 kcal/g, depending upon the equation used.The results of this experiment show that the “rapid method” for AME determinations produces highly variable dat a due to variation in voluntary intake. Although chemical methods provide a more rapid estimation of AME values than bioassays, the results obtained are not reliable.