327 Parameter Updates in the Davis Growth Model for Growth, Intake, and Composition of Modern Angus-Cross Cattle

Abstract The Davis Growth Model is a dynamic model used to estimate body composition and growth in beef cattle by simulating total DNA protein turnover. Since development parametrization the 1980s, has been re-structured account for previous rate of accretion prior nutrition. Original parameter estimates alpha (maintenance constant, where net energy maintenance x shrunk weight0.75; 0.08406) K2 (protein synthesis constant; 0.0444) may not fit modern, heavier, more productive cattle. Angus-cross steers (n = 24; initial weight 402 ± 12 kg) were fed using automated feed stations group pens (8 steers/pen). Steers high ration twice daily, at 10% greater than intake from day. measured hip height, (BW), ultrasonic measurements ribeye area back fat every 28 d until harvest (d 128). These calculate empty BW, fat, percent estimates. Parameter (± SD) 0.12661 (0.01587) 0.04919 (0.00220) K2, respectively. current study reflect large increase apparent maintenance. Maintenance requirements moderately correlated with thickness conversion efficiency. Protein turnover had very strong correlations Average efficiency was 0.17. To evaluate estimates, re-run new values K2. On average, underpredicted final 0.08 kg 0.01%-units. Considering relatively variation among observed magnitude compared those previously reported, further research required determine an accurate alpha.