Predicting Total Digestible Nutrients and Estimated Net Energy of Dairy Cow Rations from Chemical Components

Abstract

Fourteen rations varying in composition were fed in measured quantities to satisfy appetites of Holstein cows from calving through 6 or more mo of lactation. Milk yield and energy intake increased as available energy content of rations increased, but intake of dry matter was not related to milk production. The requirements for total digestible nutrients and estimated net energy of the average cow fed each ration were calculated from published requirement factors. Energy requirements were divided by amounts of dry matter consumed to calculate the total digestible nutrients and estimated net energy of dry matter consumed for each of the 14 rations. These energy values were regressed on crude fiber contents of rations either alone or with the crude protein contents to derive prediction formulas to calculate the total digestible energy or estimated net energy of rations. The following formulas had squared multiple correlation coefficients .89, .95, .85, and .93, respectively:(1)Total digestible nutrients(% of dry matter)=90.25−1.175% crude fiber(2)Total digestible nutrients(% of dry matter)=79.56−.3353% crude fiber+.7006% crude protein−.0538(% crude fiber×% crude protein)(3)Estimated net energy(Mcal/kg dry matter)=2.043−.0245% crude fiber(4)Estimated net energy(Mcal/kg dry matter)=1.837−.0057% crude fiber+.0131% crude protein−.0012(% crude fiber×% crude protein)Estimated net energy is estimated net energy as the average megacalories/kilogram of ration dry matter to support all energy needs.