Aim of the trial was to predict the net energy of lactation (NEL) of corn silage and alfalfa hay grown in the Po Valley. Five Italian university laboratories collected 120 samples of each forage during the autumn 2008 and 2009 in 16 provinces of five Italian regions (Piemonte, Lombardia, Emilia Romagna, Veneto and Friuli Venezia Giulia). Chemical contents (DM, ash, ether extract, crude protein, NDF, ADF, NDIN and ADIN) and NDF digestibility (NDFD) were determined according to NRC (2001) to calculate the NEL adjusted for a level of intake at 3×maintenance (NEL3x, NRC 2001). The NDFD was measured in vitro by using filter bags, inserted into rotating digestion jars of a Ankom DaisyII fermenter for 48 h. Chemical composition of alfalfa showed greater variability coefficients (from 14 to 20%) than corn silage (from 9 to 14%), and lower and more variable NDFD values (36.2 + 6.6 vs 49.2 + 6.6%). The average NEL3x of corn silage (1120 + 122 kcal/kg DM) and alfalfa (1484 + 84 kcal/kg DM) were similar to average tabulated values of INRA (2007) and NRC (2001). The following multiple regression equations, based on ash, NDF (% DM) and NDFD (%NDF), were obtained to predict the NEL3x contents of forages:
Alfalfa hay : NEL3x (kcal/kg DM) = (100-ash)/100 * [1499 - (16*NDF) + (13*NDFD)] R2 : 0.93
Corn silage: NEL3x (kcal/kg DM) = (100-ash)/100 * [1603 - (15*NDF) + (11*NDFD)] R2 : 0.96
Both equations allow a simpler prediction of NEL3x than those based on a complete set of chemical assays as required by NRC (2001).
