Chemical composition and standardized ileal amino acid digestibility in rapeseed meals sourced from German oil mills for growing pigs

The study was conducted to determine chemical composition and standardized ileal digestibility (SID) of amino acids (AA) in rapeseed meals (RSM) differing in glucosinolate (GSL) content for growing pigs. The selected RSM (n=5) represent the actual range in GSL content (15–5μmolGSL/gdrymatter) of commercial prepress-solvent extracted RSM among German oil mills, and were sourced from 5 different locations. In total, 5 RSM-cornstarch-based diets were formulated to contain the selected RSM as the sole protein source. The experiment was conducted according to a 5×5 Latin square design using 5 barrows with an initial body weight of 22±0.7kg, which were fitted with a T-cannula at the distal ileum. The contents of neutral detergent fiber, acid detergent fiber, acid detergent lignin and neutral detergent fiber bound crude protein (CP) increased and contents of reactive lysine (rLys) and CP, as well as ratios of lysine:CP and rLys:CP, in RSM decreased linearly as the content of GSL in RSM decreased (P<0.05). Lower GSL contents in combination with lower ratios of lysine:CP and rLys:CP indicate that over-toasting during processing of RSM may be an issue in German oil mills. There was no effect of GSL or rLys contents on SID of CP and AA (P>0.05), which is in line with the observation that the SID of AA differed not more than 7 percentage units between the 5 assay RSM. However, when taking the differences in total Lys content between assay RSM into account, standardized ileal lysine content decreased linearly from 14.2 to 11.5g/kgDM, as the GSL content decreased from 15 to 5μmol/gDM (P<0.05). Overall, SID of CP and AA in all 5 assay RSM was rather low compared with average table values for canola meal and RSM, eventually due to their relatively high contents of fiber and sinapic acid, a phenolic compound, which is associated with higher tannin contents.