Processing of soybean meal and 00-rapeseed meal reduces protein digestibility and pig growth performance but does not affect nitrogen solubilization along the small intestine

An experiment was conducted to determine the effects of processing of soybean meal (SBM) and 00-rapeseed meal (RSM) on N solubilization in chyme, CP digestibility along the small intestine, metabolic load as determined by organ weight, body composition, and growth performance in growing pigs. The SBM and RSM were processed by secondary toasting (at 95°C for 30 min) in the presence of lignosulfonate, resulting in processed SBM (pSBM) and processed RSM (pRSM) as a model for overprocessed protein sources. Fifty-four growing pigs were each fed 1 of the 6 experimental diets. Four of the diets contained SBM, pSBM, RSM, or pRSM as the sole protein source. The remaining 2 experimental diets contained pSBM or pRSM and were supplemented with crystalline AA to the same standardized ileal digestible AA levels as the SBM or RSM diet. Pigs were slaughtered at 40 kg, and organ weights were recorded. The organs plus blood and empty carcass were analyzed for CP content. The small intestine was divided into 3 segments, and chyme samples were taken from the last meter of each segment. Chyme of the SBM, pSBM, RSM, and pRSM diets was centrifuged to separate the soluble and insoluble fractions, and N content was determined in the latter. The amount of insoluble N as a fraction of N in chyme at each small intestinal segment was not affected by processing. Diet type, comprising effects of processing and supplementing crystalline AA, affected (P <0.05) the G:F and standardized ileal digestibility (SID) of CP. Processing reduced G:F from 0.56 to 0.38 for SBM and 0.49 to 0.40 for RSM, whereas supplementing crystalline AA increased G:F to the level of the SBM and RSM diets. Processing reduced the SID of CP from 87.2% to 69.2% for SBM and 71.0% to 52.2% for RSM. Diet type affected (P <0.05) the CP content in the empty body, with processing reducing this content from 170 to 144 g/kg empty BW for SBM and 157 to 149 g/kg empty BW for RSM and supplementing crystalline AA restoring this content. Processing reduced (P <0.05) the weight of several organs, and supplementing crystalline AA restored organ weight. In conclusion, processing increased the amount of N in the chyme, reduced organ weight, body CP content, and G:F. These effects were caused by a reduction in available AA as supplementing crystalline AA restored organ weight, body CP content, and G:F.