Development of equations to predict in situ rumen degradation characteristics of CP in grass silages

Between 2008 and 2013, in the GSSP project in situ rumen degradation characteristics of crude protein (CP) in approximately 100 grass silages from commercial dairy farms were measured, covering a wide range of nutrient compositions. Observed in situ CP degradation characteristics differed substantially from predictions based on current CVB rules and from values reported by ILVO. This study therefore combined datasets from GSSP, the CVB Archive, ILVO, and Schothorst Feed Research to develop improved prediction models. Stepwise regression showed that U-CP was best explained by CP and NDF, W-CP by CP, and Kd-D-CP by NDF and ash. Although the new equations predicted higher U-CP and Kd-D-CP values, calculated rumen undegradable protein (RUP) remained largely unchanged due to compensatory effects. Differences between institutes suggest methodological variation influences degradation estimates.