Metabolic characteristics of the proteins in yellow-seeded and brown-seeded canola meal and presscake in dairy cattle: comparison of three systems (PDI, DVE, and NRC) in nutrient supply and feed milk value (FMV).

To the authors' knowledge, there is little research on metabolic characteristics of the protein in newly developed yellow and brown types of canola meal and canola presscake. The objectives of this study were to (1) identify differences in the metabolic characteristics of the protein among yellow-seeded ( Brassica juncea ) and brown-seeded ( Brassica napus ) canola meal and brown-seeded (B. napus) canola presscake modeled for dairy cattle, (2) determine the extent of ruminal and intestinal digestion and absorption of the protein, (3) determine feed milk value, and (4) compare three evaluation systems in modeling nutrient supply to dairy cattle, namely, the DVE/OEB system (DVE, truly absorbed protein in the small intestine; OEB, degraded protein balance), the National Research Council (NRC) 2001 model, and the PDI system (protein truly digestible in the small intestine). Comparison was made in terms of (1) ruminally synthesized microbial protein, (2) truly absorbed protein in the small intestine, (3) endogenous protein, (4) total metabolizable protein, and (5) degraded protein balance. The results showed that there were significant differences in the truly absorbed protein supply, protein degraded balance, and feed milk value (P < 0.05) among the different types of canola meal. Yellow-seeded canola meal had significantly higher (P < 0.05) intestinal digestibility of rumen undegraded crude protein (%dRUP) than brown-seeded canola meal and presscake (%dRUP, 90 vs 75 and 60%, respectively). Yellow-seeded canola meal also had higher (P < 0.05) total metabolizable protein predicted by all three models (DVE, 312 vs 192 and 128 g/kg DM; MP, 287 vs 193 and 168 g/kg DM; PDIA, 264 vs 168 and 137 g/kg DM, respectively), lower (P < 0.05) degraded protein balance (OEB, 84 vs 104 and 102 g/kg DM; DPB, 49 vs 60 and 57 g/kg DM, respectively), and higher (P < 0.05) feed milk value (6.3 vs 3.9 and 2.6 kg milk/kg feed, respectively) than the brown-seeded canola meal and presscake. In the model comparison, the supply of endogenous protein predicted by the DVE/OEB system was higher (P < 0.05) than that predicted by the NRC-2001 model. Moreover, a high proportion of the variability in truly absorbed rumen-undegraded feed protein in the small intestine and the total metabolizable protein predicted by the DVE/OEB system was found that can be accounted for by the equivalent parameters predicted by the NRC-2001 model. The truly absorbed rumen-synthesized microbial protein values predicted from the PDI system were 19% lower than those predicted from the DVE/OEB system. Between the two latest mentioned models, no differences were detected in truly absorbed rumen-undegraded feed protein, microbial protein supply based on available energy, and degraded protein balance. All of the parameters predicted by the PDI system can be accounted for by the equivalent parameters predicted by the DVE/OEB system. When the PDI system and NRC-2001 model were compared, the overall means for microbial protein supply based on energy and truly absorbed rumen-synthesized microbial protein were found to be lower than those predicted by the NRC-2001 model. Although the factors used in quantifying calculations as well as the evaluation system's concepts differ among each other, all three protein evaluation systems employed in this study efficiently predict the potential nutrient supply to the animal from feedstuffs as affected by processing. In conclusion, the yellow-seeded canola meal provided the highest total metabolizable protein and the lowest degraded protein balance.