90 Evaluating the Difference between Formulated Dietary net Energy Values and net Energy Values Determined from Growth Performance and Estimates of Shrunk Body Weight Gain in Finishing Beef Cattle

Abstract

Abstract The California Net Energy System (CNES) was developed more than 50 yr ago and partitions energy into NEm and NEg, both of which can be calculated for feedstuffs as a cubic function of dietary ME. Recovered energy (i.e., NEg) can be calculated from NEm requirements, dry matter intake (DMI), and shrunk body weight gain (SWG). Thus, if body composition can be reliably estimated relative to maturity, SWG and DMI can be used to calculate performance-adjusted net energy values using a quadratic solution. Likewise, SWG can be predicted from 13.91 × RE0.9116 x EQSBW-0.6837. Evaluating observed vs. predicted values of NEm, NEg, and SWG enables nutritionists to better understand differences in maintenance energy requirements, efficiency of energy use, associative or antagonistic effects of feedstuffs, nutrient deficiencies, and environmental factors. Our objective was to use feedlot performance and carcass data from numerous pens of cattle fed at two locations to identify potential weaknesses in the CNES equations by evaluating factors affecting residuals between calculated dietary NEm and NEg values based on NASEM (2016) tabular values and performance based NEm and NEg values. With adjustments to address beef industry changes, the CNES will continue to maintain functionality in practical beef production.