Using the NRC chemical summary and biological approaches to predict energy values of new co-product from bio-ethanol production for dairy cows

The dramatic increase in bio-ethanol production in Canada has resulted in millions of tones of different types of new co-products: wheat dried distillers grains with solubles (DDGS), corn DDGS and blended DDGS (e.g. wheat:corn=70:30). In the determination of energy values, NRC-2001 described a chemical approach in which the equations for truly digestible nutrients are developed based on the chemical composition of native feeds. It is questionable whether this chemical approach described by NRC 2001 accurately estimates the energy values of these co-products (DDGS) for dairy cows from bio-ethanol production for dairy cows. The objectives of this study were: (1) to determine the effect of DDGS type and bio-ethanol plant on energy values (DE 3×, ME 3× NE L3×, NE m, NE g) using a biological approach (in situ assay), and (2) to investigate the relationship between the NRC chemical summary approach and the biological approach on prediction of energy values. The results showed significant effects of DDGS type on TDN 1× and energy values (DE 3×, ME 3×, NE L3×, NE m, NE g) with the highest in corn DDGS and the lowest in wheat DDGS. (2) The differences between the NRC chemical approach and the biological approach were significant for the predicted truly digestible nutrients (tdNDF, tdCP, tdFA and tdNFC). The greatest difference was found in tdNDF (-77.4g/kg DM, P<0.001) followed by tdCP (+47.9g/kg DM). Higher tdNDF was found when using the in situ assay. However, higher tdCP, tdFA and tdNFC were found when using the NRC 2001 chemical approach. (3) No differences between the two approaches (P>0.05) were detected in the TDN 1×, and energy values (DE 3×, ME 3×, NE L3×, NE m, NE g); (4) Pearson correlation analysis between the chemical approach and the biological approach showed strong relationships (P<0.05) for truly digestible nutrients, TDN 1×, and all energy values. Although the predicted energy values from the two approaches were similar, these results indicate that NRC 2001 chemical summary approach was different from the biological approach (in situ assay) in prediction of tdNDF and tdCP for bioethanol co-products, indicating that a refinement of the NRC 2001 formula to predict tdNDF and tdCP is required for these products.