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Formulating Beef Rations with Varying Levels of Heat Increment

Economic Research Service, U.S. Department of Agriculture 20250

Abstract

A theoretical framework for blending rations to improve performance of beef cattle under heat or chill stress is presented. The framework and computational procedures used involve a systematic variation of the heat increment in rations with constant amount of net energy for maintenance and net energy for gain. The heat increment of a ration is useful for maintenance of body temperature in chill stress, but is burdensome and must be eliminated in heat stress.

The energy system used employs three equations, two of which are the net energy equations of the Lofgreen-Garrett net energy system. The third equation is for metabolizable energy. The solution requires techniques developed earlier by the author for the Lofgreen-Garrett system along with parametric programming on metabolizable energy so as to vary indirectly the heat increment. Two sets of three rations with the maximum, minimum and intermediate levels of HI were obtained. The rations were designed so that expected gains under thermal neutrality for a steer weighing 365 kg was 1.4 kg per day for the first set of three rations and 1.3 kg per day for the second set. The maximum, minimum and intermediate levels of HI in Meal obtained were 13.79, 10.23 and 13.17, respectively, for the first set and 13.45, 9.67 and 12.84, respectively, for the second set. Comparisons under different assumed environmental conditions indicate how much improvement in animal performance can be obtained by changing the rations when environmental stress occurs. Economic analysis indicates that the increased ration cost of adjustments in HI to meet stress conditions can be more than offset by the benefits of the resulting improvement in performance. Whether this is so depends on ingredient prices, the degree of stress and how the animal adjusts feed intake when stress conditions occur.

¹ The author is grateful to Richard E. Vaile, Gene Nelson, and Dale Waldo, for helpful comments on earlier drafts of this paper. Also, educational discussions and references on energy metabolism were provided by Paul W. Moe, W. N. Garrett, G. P. Lofgreen, D. C. Church, R. A. Ralston and Peter R. Cheeke.