Factors Influencing Energetic Efficiency of Beef Production

Abstract

The relation between retained energy (RE) and metabolizable energy (ME) intake, together with the convention which separates maintenance and production functions, forms the basis for a discussion of energetic efficiency of beef cattle. The efficiency of ME use for maintenance (km) and for gain (kg) are related to the source of the ME. Over the range of ME found in most feedstuffs and mixed diets (2.0 to 3.0 kcal/g), km increases by about 10 percentage units and kg by about twice that amount. The composition of the gain also seems to be an important determinant of kg. Estimates of the efficiency of the ME utilization for fat deposition in ruminants have been high (60 to 80%). Net protein deposition is much less efficient, with estimates in the 10 to 40% range. Variations in the efficiency of ME utilization for whatever reason can create problems when a general system of feed evaluation is used for a specific practical situation. In the future, feeds may be evaluated, diets formulated and animal response predicted, not from net energy or ME values, but from a detailed chemical and physical description of each feed and a knowledge of the biochemical, physiological and physical processes involved in animal metabolism.