True and standardized ileal digestibilities and specific ileal endogenous recoveries of crude protein and amino acid in soybean meal, rapeseed meal and peas fed to growing pigs

A digestibility study was conducted to investigate true (TID) and standardized (SID) ileal digestibilities and specific ileal endogenous recoveries of crude protein (CP) and amino acids (AA) in pigs fed cornstarch-based assay diets with soybean meal, rapeseed meal or peas. The TID and total ileal endogenous CP and AA recoveries were determined using the homoarginine (Harg) method. Six barrows (German Landrace × Pietrain) with an initial body weight of 19 ± 1.8 kg, and fitted with ileal T-cannulas were fed the assay diets according to a double 3 × 3 Latin Square design. The assay diets were formulated to contain 180 g CP/kg (as fed basis). Ileal digesta were collected continuously for 24 h to determine SID values on days 6 to 8 and for 12 h to determine TID values on days 9 to 10 of each experimental period. The TID and total ileal endogenous recoveries were determined by feeding assay diets with 50% of the dietary protein source guanidinated to convert Lys to Harg for direct determination of TID of Lys. Total ileal endogenous Lys and CP recoveries (g/kg DMI) were highest (P < 0.05) in ileal digesta of pigs fed the pea compared to the rapeseed meal or soybean meal assay diets. By contrast, recoveries of specific ileal endogenous CP and most AA (g/kg DMI) in the assay feed ingredients were higher in soybean meal compared to rapeseed meal (P < 0.05) and intermediate for peas (P > 0.05). The TID of CP and AA were the lowest (P < 0.05) in rapeseed meal compared to soybean meal or peas. The lowest SID of CP and indispensable AA were observed in rapeseed meal, with intermediate values for peas, and highest values in soybean meal (P < 0.05). As specific ileal endogenous recoveries differ among feed ingredients, these losses should be considered explicitly in addition to SID values to account for the metabolic costs associated with the intestinal synthesis and recycling of endogenous CP and AA.