Nutrient analysis, metabolisable energy and ileal amino acid digestibility of palm kernel meal for broilers

• Although PKM is a poor protein source, its AA digestibility values are moderate.
• Protein digestibility value is not a good indicator of AA digestibility of PKM.
• Direct method underestimates AA digestibility of low-protein content feedstuffs.

Nutrient composition, apparent metabolisable energy (AME) and ileal amino acid (AA) digestibility of palm kernel meal (PKM) were evaluated using laboratory analyses and animal studies. The AME assay was conducted with broilers using the classical total excreta collection between d 18 and 25 post-hatch. A maize-soy basal diet was formulated and a test diet, containing PKM, was developed by replacing (w/w) 250 g/kg of the basal diet with PKM. The AME of PKM was calculated based on the difference between the AME values of basal and test diets. Ileal AA digestibility of PKM was determined using two methods, namely direct and difference methods. In the direct method, the assay diet was formulated with the PKM serving as the sole source of AA. In the difference method, the basal and test diets used in the AME assay were used. All diets (both methods) contained titanium dioxide as an indigestible marker. The ratios between the titanium and AA in the diet and digesta were used to calculate the digestibility. The crude protein and fat contents of the PKM sample were 159 and 94.0 g/kg, respectively. The AME and nitrogen-corrected AME of PKM were determined to be 5.47 and 5.23 MJ/kg, respectively. The assay method had no effect (P > 0.05) on the ileal digestibility of protein, but influenced (P < 0.05–0.001) the digestibility of all AA except tyrosine (P > 0.05). Standardised ileal AA digestibility coefficients determined by the difference method were higher than those determined by the direct method. The present data showed that the use of direct method will underestimate the ileal AA digestibility coefficients of feedstuffs with low-protein content.