Therefore, biological attributes of a feed have much greater meaning in predicting the productive response of animals but are more difficult to accurately determine because there is an interaction between the chemical composition of a feed with the digestive and metabolic capabilities of the animal being fed. Biological attributes of feeds are more laborious to determine and are more variable than chemical constituents. They are generally more predictive, however, since they relate to the response of an animal being fed the feed or diet. Where information was not available but a reasonable estimate could be made from similar feeds or stage of maturity, this has been done since it is not too helpful to have a table with considerable missing information. Where zeros appear, the amount is so small that it can be considered insignificant in practical diet formulation.
Blanks indicate that the value is unknown.
The table this year contains revisions as well as values for feeds that were not included in previous tables. For this reason, chemical constituents and biological attributes of feeds shown in the table are on a DM basis. Four measures of the energy value of feeds are shown in the table. There are several technical problems with TDN, however. TDN also overestimates the value of roughages compared to concentrates in producing animals.