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- Title
Performance by feedlot steers and heifers: Daily gain, mature body weight, dry matter intake, and dietary energetics.
- Authors
Zinn, R. A.; Barreras, A.; Owens, F. N.; Plascencia, A.
- Abstract
Performance, DMI, diet composition, and slaughter data from 9,683 pens of steers and 5,009 pens of heifers that were fed high-concentrate diets for 90 d or more were obtained from 15 feedlots from the western United States and Canada. The data set included pen means for more than 3.1 million cattle fed between 1998 and 2004. Performance measurements assessed included ADG, DMI, dietary NE, shrunk initial weight (SIW), and shrunk final weight. Mature final weight (MFW) for cattle in each pen was estimated based on regression of slaughter weight against SIW and ADG across all pens. Equations were developed to standardize performance projections (ADG, MFW, and break-even values) and analyze feedlot cattle close-outs. Generally, as diet NE concentration increased, DMI was decreased but G:F, dressing percentage, and yield grade all increased. Pens of cattle with greater SIW had greater ADG, DMI, and shrunk final weight but a lower G:F and dressing percentage. Dressing percentage and yield grade were correlated positively. Equations of the NRC relating gain to NE intake explained 85 and 80% of the variation in DMI of steers and heifers, respectively, with mean ratios of predicted to observed DMI (DMIratio) at 1.000 ± 0.0506 and 0.974 ± 0.0490. However, a significant (P < 0.001) bias in the NRC estimate of DMI was detected (r² = 0.10 and 0.05, for steers and heifers) between the DMIratio and ADG in which DMlratio increased as ADG increased. This was due to inherent confounding of ADG and MFW in the original NE equation of Lofgreen and Garrett. Based on iterative optimization to minimize the difference between expected and observed DMI, revised equations for retained energy (RE, Mcal/kg) were developed for steers and for heifers: REsteer = 0.0606 × (LW × 478/MFWsteer)0.75ADG0.905 REheifer = 0.0618 × (LW × 478/MFWsteer)0.75ADG0.905, where LW = mean shrunk live weight. The revised equations decreased the SD of the DMIratio by 5.4% (from 0.0496 to 0.0469) and eliminated the bias in DMlratio that was related to ADG (r² = 0.0006). The similarity between the 2 equations derived for steers and for heifers for estimation of RE from ADG supports the concept that scaling by MFW accounts for energy utilization differences between sexes.
- Subjects
FEEDLOTS; FACTORY farms; BEEF cattle; HEIFERS; COWS; BOVINE anatomy
- Publication
Journal of Animal Science, 2008, Vol 86, Issue 10, p2680
- ISSN
0021-8812
- Publication type
Article
- DOI
10.2527/jas.2007-0561