Influence of nutrition level on digestibility in high yielding cows and effects on energy evaluation systems.

The objective of the study was to determine the effect of nutrition level (NL, multiples of maintenance energy requirement) on the digestibility of nutrients for dairy cows regarding the energy supply of the animal. The digestion of nutrients and energy was investigated in two trials using lactating dairy cows. The NL varied from 2.7 to 5.0 using diets similar composition. In addition, sheep were given the same feed with a NL of 1.4. Digestibility of dry matter (DM) and all specific measures of dietary components declined significantly as NL increased. Digestibility of energy decreased by 4.1% for each increase in NL. The metabolizable energy, the ability to metabolize energy (metabolizable energy/gross energy), and the content of net energy for lactation (NE(L)) per kilogram of DM intake were calculated for NL from 1 to 6 on the basis of these relationships and as well as the gross energy, methane energy, and urine energy. Accordingly the NEL content declined by 0.11 MJ/kg of DM intake or 1.6% as the NL increased by one unit. It means that the NE(L) requirement above the maintenance requirement increased by 0.07 MJ of NE(L) per kilogram of fat-corrected milk, if the NL increased by one unit.