An audit of the current U.S. Department of Agriculture frame size scoring system

Feedlot and carcass data from steers (n = 16,700) and heifers (n = 6,357) originating from 16 different states and fed in 17 feedlots located in southwest Iowa were used to evaluate the accuracy of the USDA frame score for predicting final BW of fed cattle. Frame score was recorded by USDA or state personnel for cattle either before leaving the state of origin or on arrival at the terminal feedlot. Mixed model procedures were used to investigate relationships between USDA frame score and measures of live performance and carcass traits. Other fixed effects included in the model included USDA muscle score, sex, age classification on feedlot entry (calf: ≤270 d of age, yearling: 271-365 d of age, and long yearling: >365 d of age), BCS on feedlot arrival, number of treatments for respiratory disease, hide color, and site of frame or muscle scoring; the interactions of sex × frame score and hide color × frame score were also included; fat thickness was included as a fixed effect (covariate) in the analysis of ADG, final BW, days on feed, LM area, marbling score, and quality grade. Random effects included in the model were year of feedlot arrival and feedlot in which cattle were fed. The system accurately projects the minimum target final BW for large frame steers and heifers; however, the final BW of the smallest medium frame steers and heifers exceeds the target minimum final BW by 35 and 40 kg, respectively. When frame score was assigned post facto based on actual final BW (adjusted to 1.27 cm fat thickness), it was determined that large frame was over-assigned by graders (62 vs. 35% for steers and 54 vs. 32% for heifers, actual score vs. postharvest score, respectively), medium frame was underassigned (37 vs. 51% and 46 vs. 58% for steers and heifers), and small frame was underassigned (0.7 vs. 15% and 0.6 vs. 10% for steers and heifers; K = 0.01, P < 0.01). Across sexes, of the cattle assigned to small, medium, or large frame score, 40, 59, and 43% actually had final BW (adjusted to 1.27 cm fat thickness) within the guidelines for the target final BW of each of the frame scores (P < 0.01). The present frame score system accurately reflects the modern feedlot cattle population; however, adjustments in the assignment of frame scores to reflect changes in technologies and final weights may be warranted.