Modeling nutrient supply to dairy cattle from a feedstuff using NRC-2001 (a TDN-based model) with inputs based on in situ and mobile bag technique measurements

Abstract

The objectives of this study were to use the NRC-2001 model with inputs based on in situ and mobile bag techniques to (1) predict the potential nutrient supply to dairy cows using an exampled feed- whole lupin seeds that were systematically toasted and (2) quantitatively determine the effects of toasting (which shifted degradation of protein from the rumen to the abomasum and small intestine without changing intestinal digestion) and optimal toasting conditions by the NRC-2001 model. The quantitative predictions were made in terms of: (1) rumen undegraded and degraded feed protein, (2) truly absorbed undegraded protein, (3) potential microbial protein synthesized in the rumen from rumen available protein or (4) from total digestible nutrients (TDN), (5) truly absorbed rumen synthesized microbial protein, (6) truly absorbed rumen endogenous protein, (7) total metabolizable protein (MP), as well as (8) the protein degradation balance (PDB). The results show that using the NRC-2001 model with inputs based on in situ and mobile bag techniques, the predicted PDB and MP supply to dairy cattle was significantly improved. However, no optimal condition could be obtained from this study due to high PDB values (>48 g kg-1 DM) in all the treatments, predicted by the model. With toasting, temperature and/or duration could go still higher than 136°C and/or longer than 15 min to further prevent potential N loss in the rumen if total tract digestion is not depressed. More study is needed. However, the results differed from that published with the DVE/OEB system (a non-TDN-based model) although the two models had significant correlations with high R (>0.99) values. Using the NRC model, the overall mean for MP was higher (+10 g kg-1 DM), but the PDB values were lower (-12 g kg-1 DM) in comparison with that predicted by the non-TDN based model for the whole lupin seeds. Key words: Modeling nutrient supply, dairy cattle; National Research Council, in situ, mobile bag technique