Estimating In Situ Effective Crude Protein Degradability with Cornell Net Carbohydrate and Protein System Parameters in Energy-Rich Feedstuffs for Ruminants

The objective of this experiment was to estimate in situ effective crude protein degradability (EPD) with Cornell Net Carbohydrate and Protein System (CNCPS) parameters [crude protein fractions (A, B-1, B-2, B-3 and C) and degradable protein intake value (DIP) values] of six energy-rich feedstuffs. Four cereals: maize, wheat, barley, rye and two wheat middling (WM-1 and WM-2) were tested. The in situ effective protein degradability (EPD) was calculated using the nylon bag method where the test feedstuffs incubated in the rumen of three Tahirova wethers. The EPD's were estimated as EPD2, EPD5 and EPD8 assuming rumen outflow rates of 0.02, 0.05 and 0.08 h(-1). The crude protein fractions i.e. A=NPN, B-1=fast, B-2=intermediate, B-3=slow and C=not fermented and unavailable to the animal were calculated using the soluble protein (SolP), the non-protein nitrogen (NPN, % of SolP), the neutral detergent insoluble protein (NDIP) and the acid detergent insoluble protein (ADIP=C) values of feedstuffs based on CNCPS. Then, DIP was calculated by using CNCPS crude protein fractions, degradation rate of B fractions (Kd) and coefficients of outflow rate on the different levels of dry matter intake (Kp): (DIP1X=at 1x maintenance level of intake, DIP2x=at 2x maintenance level of intake, and DIP3x=at 3x maintenance level of intake). It was found that there was a significant multiple regression relation between the EPD8 (g/kg DM) and crude protein fractions (g/kg DM) (R-2=0.96, n=18, P<0.001), and simple regression relation between the EPD8 (g/kg DM) and DIP3X (g/kg DM) (R-2=0.98, n=18, P<0.001). These regression relations did not improve when the different rumen outflow rates were used to estimate EPD. In conclusion, we claimed that in situ effective protein degradation (EPD) can be reliably and accurately predicted from CP fractions and DIP values in cereals and wheat middling.