Fact Sheets no. The California Energy System is the best present system for predicting growing-finishing cattle performance from the rations they are being fed. The net energy requirements of growing cattle are related to body weight, stage of growth for a given weight, rate of gain, sex, environmental conditions, age and nutritional history. To use this system accurately, one must know NEm and NEg of the ration, animal sex, weight and feed intake. Net energy is the net quality of energy recovered or retained in an animal product.
Retained energy can be a negative quantity for animals fed below their maintenance requirements.
The use of net energy as a base for feed evaluation is complicated by available metabolizable energy from the animal's diet. These complications have been partially accounted for in a net energy system for beef cattle that assigns two net energy values to each feedstuff. Animal requirements for energy are similarly subdivided. That is, they do not have to be adjusted for different roughage-concentrate ratios. Feed requirements for maintenance are estimated separately from feed needed for the productive functions.