Our example would require a total of 3.23 MJ of ME (1.89 MJ for maintenance and 1.34 MJ for gain). Total ME requirement is the sum of ME
m and ME l-d
This does consider 1) use of dietary ME for tissue accretion or 2) use of mobilized tissue energy for milk production. In other words, a doe gaining weight will require more ME than based simply on milk production and fat concentration. Likewise, a doe losing BW will require less dietary ME for a given quantity and composition of milk than predicted above.
For 1), need to multiply positive ADG (g) by 0.0239 MJ/g and then divide by an efficiency of 0.75 to estimate dietary ME used for tissue accretion (e.g., 20 g ADG x 0.0239 MJ/kg / 0.75 = 0.637 MJ/day of dietary ME required for this 20 g ADG. Assuming a dietary ME concentration of 10.0 MJ/kg dry matter (i.e., 2.4 Mcal/kg), 64 more grams of dietary dry matter would be required).
For 2), need to multiply negative ADG (g) by 0.0239 MJ/g and then multiply by an efficiency of 0.84 to estimate milk energy arising from mobilized tissue ME (e.g., 20 g ADG x 0.0239 MJ/kg x 0.84 = 0.402 MJ of milk energy arising from this 20 g/day of body weight (BW) loss, which equates to 0.131 kg of 4%-fat corrected milk). Likewise, this 0.402 MJ of milk energy equates to 0.683 MJ of dietary ME (calculated assuming an efficiency of use of MEl-d for lactation of 0.589). So, for example, if you estimated that 2.0 kg of dry matter had to be consumed for a certain level and composition of milk production, and with a dietary ME concentration of 10.0 MJ/kg dry matter (i.e., 2.4 Mcal/kg), if the doe was mobilizing 20 g of BW each day, she would need to consume 68 g less of the diet than estimate assuming no change in BW.
The total ME requirement can then be divided by the dietary ME concentration to determine the required level of dry matter intake. Because of efficiencies of ME use for maintenance and lactation not greatly different from one another, application of a correction factor to account for differences in efficiencies of ME use among diets and levels of intake is not necessary.