Partitioning Energy Requirements of Angus, Charolais and Reciprocal Cross Cows

Increasing energy costs have stimulated more interest in efficient use of our natural resources. Utilization of energy in agricultural enterprises needs to be critically evaluated for economic survival of the enterprise. Feed energy required for beef production comes largely from harvested and unharvested forage and grasses constitute a high proportion of the costs of maintaining a cow. These costs have increased along with other production inputs. Beef cattle producers need to know how total feed energy is utilized in order to increase their efficiency. Cow herd efficiency is extremely important, especially the energetic efficiency of various size groups. Knowing the proportions of feed required for maintenance, growth of body tissue and production will assist the progressive producer in evaluating the efficiency of is cattle. Economic pressure on beef producers necessitates critical evaluation of all production costs. The goal of cattlemen is to produce beef for the table by the most profitable method. Feed constitutes the largest variable expense in the beef enterprise. Energy provided by feed can theoretically be divided into parts for maintenance of body weight, growth of body tissue and production of animal products. Optimum performance of a cow is related to the proportion of energy utilized for each partition. Cow herd efficiency is extremely important, especially the energy efficiencies of various cow sizes. Differences in overall efficiency of feed used may be due to differences in maintenance requirements or nutrient utilization. Knowledge of amounts of feed required for each use is needed to predict economic consequences of feeding and management systems. Although cow size has little effect on efficiency, recent interest in larger cows suggests a need for an accurate method of predicting energy requirements for large and small cows during the different stages of production. The objective of this study was to partition the energy intake of Angus, Charolais and reciprocal cross cows into maintenance, weight change and milk production. Equations were developed to predict TDN (total digestible nutrients) requirements for beef cows and replacement heifers over a range of weights and during different stages of production