Metabolizable energy and amino acid digestibility of mash and pelleted diets for broilers determined under different methodologies

The objective of this study was to determine the interaction between feed processing and different methodologies for assessing apparent metabolizable energy corrected by nitrogen (AMEn) and standardized ileal digestibility coefficients (SIDC) of amino acids (AA) in broiler diets. A completely randomized design in a 4 × 2 factorial was used to evaluate AMEn by four methodologies and two physical forms of diet (mash and pelleted). The methodologies were total excreta collection and use of the markers: acid insoluble ash (AIA), titanium dioxide (TiO2) and chromium oxide (Cr2O3). After 5 days of total excreta collection, all the birds were slaughtered and ileal content was assessed for AA. There was significant interaction (P < 0.05) between the methodologies and physical form of the diets on AMEn values. Regardless of the physical form of the diet, the AIA marker provided similar AMEn values for total excreta collection on a DM basis. Pelleted diets had higher values (P < 0.05) of AMEn (MJ/kg) on DM, except for Cr2O3. For AA, there was no interaction (P > 0.05) between the markers and the physical form of the diets. There was no difference in SIDC between mash and pelleted diets (P > 0.05). The AIA marker provided a higher SIDC compared to the TiO2 and Cr2O3 markers, except as regards methionine and lysine. Overall, pelleting increases dietary AMEn, but does not affect amino acid digestibility. Total collection and AIA lead to similar AMEn values, and AIA provides higher SIDC of the amino acids.