Detergent fiber traits to predict productive energy of forages fed free choice to nonlactating dairy cattle.

Hay crops that were predominantly alfalfa, clover or grass, and silage corn were harvested at early and late maturities to give a wide range in fiber contents. Hay crops were stored as field-cured hay and wilted silage. Each was fed for ad libitum intake to three or more nonlactating Holstein animals using total collection digestibility and calorimetry to measure DM intake, TDN, digestible energy, and metabolizable energy. Various fiber components (ADF, NDF, lignin), and expressions computed from them, were used to estimate TDN and digestible energy of forages or groups of forages having homogenous relationships. Stepwise backward elimination procedure was employed to discard independent variables or their squared terms at 5% probability to develop significant, biologically sound, practical predictive relationships. Standard NRC equations were used to extend energy densities to NEL. Free choice DM intake of forages (fed alone) was not closely related to NDF percentages. Estimates of NEL generally were higher when computed via TDN as opposed to digestible energy or metabolizable energy, which did not differ. We present equations to predict NEL from ADF via digestible energy for legumes, grasses, and corn silage, which differ markedly, in some cases, from those in current use. Equations for grasses had low r2, but these could not be compared with published ones, which apparently are based on treatment means rather than individual-animal observations. The NEL of hay crops and corn silages also were predicted from an expression of lignified NDF in DM with moderate precision.