A System for Expressing Net Energy Requirements and Feed Values for Growing and Finishing Beef Cattle

A proposed system is presented for expressing net energy requirements and feed values for growing and finishing beef cattle. The system uses one expression, NEm, to represent the net energy requirement and the net energy content of the feed when used for maintenance and a second expression, NEg, for the net energy used for production of weight gain. Data from comparative slaughter trials indicate the NEm requirement for both steers and heifers is equal to approximately 0.077 megcal. per unit of metabolic body size (W0-7kg.). The energy deposited in the weight gain of steers (the NEg requirement) is represented by the equation NEg=52.72g+6.84g2 where NEg is the kcal. of energy deposited per day per unit of W0-75kg. and g is the daily empty weight gain in kg. The equation for heifers is NEg= 56.03g+12.65g2. It was shown that heifers deposit more energy per unit of weight gain than do steers and that the difference is larger at higher rates of gain. Data are presented demonstrating that the proposed system is adaptable to practice and that it overcomes the common criticisms that net energy values do not apply under maintenance conditions and vary with feed intake.