Digestive and metabolic impact of using extruded-expelled soybean meal as a protein source for sheep fed with a total mixed ration

This study aimed to evaluate the effect of including extruded-expelled soybean meal (ESBM) as the main protein source in a total mixed ration (TMR) offered to sheep on digestive and metabolic parameters, in comparison to protein sources with known nutritional properties: solvent-extracted soybean meal (SBM; high ruminal degradability) and dried distillers grains with solubles (DDGS; low ruminal degradability). Five Corriedale × Suffolk crossbreed male sheep (33.7 ± 4 kg body weight) fitted with ruminal catheters and duodenal cannulas were used in an incomplete double 3 × 3 Latin square design, comprising three experimental periods of 20 d each. On a dry matter basis, the TMR was composed of corn silage (0.60) and a mixture of concentrate feedstuffs (0.40), which included ground corn and one of three protein sources: ESBM, SBM, or DDGS. The sheep receiving TMR with ESBM showed intermediate organic matter digestibility compared to SBM and DDGS and lower neutral detergent fibre digestibility together with DDGS (<i>p</i> <0.05). Rumen fermentation and digestion variables were similar between ESBM and SBM, but the N use efficiency tended to be higher in ESBM (<i>p</i> <0.08). Compared to ESBM and SBM, DDGS decreased the N digestibility, the concentrations of ruminal ammonia-N and the urinary N losses, and increased the duodenal flow of non-ammonia non-microbial N (NANMN) and α-amino N (<i>p</i> <0.05). In conclusion, replacing SBM with ESBM in TMR offered to sheep did not impact most of the rumen fermentation and digestion variables whereas improved the efficiency of N utilisation. In contrast, replacing SBM with DDGS in TMR for sheep has been shown to reduce N losses through urine, increase the duodenal flow of dietary N, and improve N utilisation efficiency.