from that of birds fed diets containing MBM 2 and 5. The only plausible reasons for this may be a result of poor AA quality of the processing conditions or of the quality of the fat in the MBM sample. Generally, values from the 7 MBM samples are similar to what was earlier reported for 4 MBM samples from different source fed to 21-d-old broiler chickens (Adedokun et. al., 2007b). Furthermore, values reported for conventional and cecectomized roosters by Parsons et al. (1997) were higher than those obtained in the current study. Although not measured in this study, the mean retention time or the digesta passage rate is another factor that may have influenced the results obtained from the MBM samples used in this study. It is possible that the interaction between the different MBM components could have resulted in varying digesta speed across the gastrointestinal tract. The mean retention time of a particular feed could affect how much of the nutrients in a feed are digested and absorbed. McNab (1994) reported that the physical characteristics and the chemical components of the diet (as a result of the ingredients composition of the diet) may affect the degree of nutrient utilization and this may, to some extent, depend on the digesta passage rate (Mateos and Sell, 1980; Rochell et al., 2012; Kong and Adeola, 2013). In summary, SIAAD values from MBM are quite variable, and the capacity of 21-d-old broilers and 30-wk-old laying hens for AA digestion and absorption from MBM from different sources are quite variable, with broilers showing greater capacity for AA digestibility. This shows that a need exists to procure MBM from a consistent and reliable source so as to minimize variability in AA digestibility and, hence, birds’ performance. Data generated from this study could be used in formulating broiler and laying hens’ diets on a digestible AA acid basis. Formulation on a digestible AA basis may reduce cost, reduce N and AA excretion, and increase flock uniformity and returns on investment; but it is important to realize that data from a broiler database for ingredient digestibility may not always be applicable to that of laying hens. Finally, as the role of difference in Ca and P requirements for 21-d-old broilers and adult laying hens were not factored into the design of this study, it may be necessary to further investigate the short time effect of dietary Ca and P on ileal AA digestibility of MBM from different sources.