Effect of ileum segment and protein sources on net disappearance of crude protein and amino acids in laying hens.

1. This study investigated the net disappearance of crude protein (CP) and amino acids (AA) from soybean meal and rapeseed meal in different sub-sections of the ileum of hens. A basal diet was used and in another 4 diets, maize starch contained in the basal diet was replaced with soybean meal or rapeseed meal at 140 and 280 g/kg so that changes in dietary AA concentrations resulted from the oilseed meals only. 2. A total of 250 Lohmann Brown pullets were used for this experiment at 20 weeks old and given one of the 5 diets for 7 d. The section between Meckel's diverticulum and 2 cm anterior to the ileo-caecal-colonic junction was taken after slaughtering the hens and cut into three sub-sections of equal length. Digesta were taken separately from each sub-section and then frozen. Net disappearance of AA and CP for the diets and the two protein sources was calculated based on standard equations and using a multiple linear regression approach. 3. Net disappearances of CP and all AA were significantly lower in the proximal sub-section than in the central and terminal sub-sections. Also, the net disappearance of CP and all AA from rapeseed meal was significantly lower in the proximal sub-section than in the central or terminal sub-sections. For soybean meal, only the net disappearances of arginine, aspartic acid, glutamic acid and phenylalanine were significantly lower in the proximal than in the terminal sub-section. No significant differences in the net disappearance of CP and AA were detected between protein sources within the central and terminal sub-sections or between the central and terminal sub-section within each protein source. Soybean meal had a significantly higher net disappearance of CP and AA (with the exception of cystine and methionine) than rapeseed meal in the proximal sub-section but these differences were not statistically significant in the central and terminal sub-sections. 4. Amino acids disappeared from the proximal region of the ileum. This needs consideration in standard approaches that are used for measuring AA digestibility. There is a variation in AA digestibility between soybean meal and rapeseed meal. The ranking of individual AA regarding their digestibility is different between the two oilseed meals.