Freeze Drying Versus Oven Drying of Excreta in True Metabolizable Energy, Nitrogen-Corrected True Metabolizable Energy, and True Amino Acid Availability Bioassays

The effect of excreta drying procedure on resulting true amino acid availability (TAAA), true metabolizable energy (TME), and nitrogen-corrected TME (TMEn) values was investigated using two high-protein feedstuffs. The TAAA and TME assays were based on those of Likuski and Dorrell (1978) and Sibbald (1976), respectively. Twenty-five grams of either dehulled soybean meal (SBM) or poultry offal meal (POM) was administered to White Leghorn roosters. Excreta samples were divided, one portion being freeze dried and the other dried in a forced air oven at 60 C. The TAAA, TME, and TMEn values, based on the excreta samples from the different drying procedures, were compared. No significant differences (P≤.05) in the TME or TMEn of either ingredient could be attributed to drying technique. It is concluded that the capability to freeze dry excreta is not a prerequisite to the successful use of the TME and TMEn bioassays. The availability of the total of amino acids in the test ingredient was similarly unaffected by drying technique; however, for several individual amino acids, including lysine and arginine in both ingredients, methionine in SBM and valine in POM, values were significantly higher when excreta were oven dried. This suggests either a limited destruction or irreversible binding of these amino acids during oven drying.