Prediction of protein supply to ruminants from concentrates: comparison of the NRC-2001 model with the DVE/OEB system

The objective of this study was to compare the DVE/OEB system (DVE = truly absorbed protein in the small intestine; OEB = degraded protein balance) and the NRC-2001 model in the prediction of supply of protein to dairy cows from 46 selected concentrates: malting-type barley (cv Harrington), feedtype barley (cv Valier), field tick beans (Vicia faba), white albus lupins (Lupinus albus), whole soybeans and horse beans (Vicia faba cv Alfred). The two barleys were processed by coarse (roller miller, 0.533 mm gap) and fine (hammer mill, 2 mm screen) processing. The field tick beans and white albus lupins were dry roasted at various conditions at the University of Melbourne. The soybeans and horse beans were pressure-toasted at 100, 118 and 136degreesC for 3, 7, 15 and 30min at Wageningen Feed Processing Centre. Comparisons were made in terms of (1) ruminally synthesized microbial protein, (2) truly absorbed protein in the small intestine and (3) degraded protein balance, based on 46 samples. The results showed that the predicted values from the DVE/OEB system and the NRC-2001 model had significant correlations. However, using the DVE/OEB system, the overall average microbial protein supply based on available energy was 10% lower and the truly absorbed protein in the small intestine was 8% lower than that predicted by the NRC-2001 model. A difference was also found in the prediction of the degraded protein balances, which was 16% higher than that estimated from the NRC-2001 model. These differences are due to factors used in calculations in the two models, although both are based on similar principles. This indicates that further refinement is needed for a modern protein evaluation and prediction system. (C) 2004 Society of Chemical Industry.