Protein value of a new genotype oat (CDC SO-I) for the NRC dairy model: Protein degradation balance and kinetics, protein fractions and total metabolizable protein supply

Abstract

Recently, a new genotype of oat has been developed specifically for feed purposes by the Crop Development Centre called CDC SO-I (“SuperOat”) containing a low-lignin hull and a high-fat groat. However, no quantitative evaluation of protein supply from CDC SO-I to dairy cow has been done in terms of potential protein degradation balance (PDB) and total metabolizable protein (MP) supply. These data are crucial in order to develop more efficient, competitive and optimal feeding the new genotype of oat (CDC SO-I) for livestock. Unlike DVE/OEB, PBI, ARC and NKJ-NJF models, NRC-2001 is a total digestible nutrient (TDN-) based model which is more popular in North America. The objectives of this study were to use the NRC model with inputs based on laboratory and in situ techniques to predict the potential nutrient supply to dairy cows from CDC SO-I in comparison with two conventional oat varieties, CDC Dancer and Derby, in western Canada. The quantitative predictions were made in terms of: (1) Rumen-synthesized microbial protein truly absorbed in the small intestine (AMCP); (2) Rumen undegraded feed protein truly absorbed in the small intestine (ARUP); (3) Endogenous protein in the digestive tract (AECP); (4) Total metabolizable protein supply in the small intestine (MP), and (5) Protein degraded balance (PDB). The results show that using the NRC model, the predicted PDB and total MP supplies to dairy cattle were significantly increased from the newly developed genotype of oat (CDC SO-I). Compared with the normal oat, CDC Dancer, CDC SO-I significantly increased (P < 0.05) ARUP, by 24%, and total MP supply by 9%, but did not change (P > 0.05) AMCP, AECP and PDB, with averages of 55.7, 4.5 and -11.96 g kg-1 dry matter (DM), respectively. Compared with the normal variety, Derby, CDC SO-I significantly increased (P < 0.05) AMCP, by 19%, total MP supply by 13% and increased PDB by 114%, but did not change (P > 0.05) ARUP and AECP values with averages of 19.2 and 4.5 g kg-1 DM, respectively. In conclusion, CDC SO-I oat increased total absorbed metabolizable protein supply to dairy cattle by 9–13% in comparison with the two conventional oat varieties used in western Canada. However, although CDC SO-I improved protein degraded balance, it still had a negative value (-10.6 g kg-1 DM), indicating the potential imbalance between microbial protein synthesis from available rumen-degradable crude protein (CP) and potential energy from fermentation in the rumen. Key words: TDN-based model, dairy cattle, oat genotype, protein degradation balance, metabolizable protein supply