Applying Energy Values in Formulating Rations DE, TDN and ME are related, and one value is used to estimate the others, as the major factors that affect one also affects the others. It is more difficult to directly relate these to NE, however, because of the extreme variation in heat loss from one feed to another. This is illustrated by the fact that 1 pound of TDN from corn contains more NE than does 1 pound of TDN from hay, primarily because TDN does not take into account the difference in heat loss per unit of TDN or ME, as previously discussed. NE adjusts for the variation in heat loss as well as the other energy losses, making NE values more consistent from one feed to another. This alfalfa is worth 53 percent as much as the corn for maintenance, 0.55 divided by 1.04, but only 31 percent as much as the corn for growth, 0.21 divided by 0.67.
Separation allows a more accurate prediction of gains from a given combination of feedstuffs.
The hay should be used in the maintenance or wintering type ration and the corn in the finishing ration where both types of feeding programs are being used. When appropriate net energy values are assigned to the feedstuffs used in the ration and the ration is balanced for all other nutrients, gains predicted from the feed consumed will usually be within 5 to 10 percent of actual gains. Factors such as extremes in weather and cattle, variations in quality of feedstuffs, pen conditions and compensatory growth will reduce the predictability of gains. One of the greatest problems is to assign proper NE values to the feeds used. More research is needed to properly define the NE m and NE g values of various feeds, particularly forages, under various environmental conditions.