RESUMEN
Our study aimed to evaluate the frame size as a genetic selection criterion as well as the association of scores with carcass characteristics measured via ultrasound to the genetic improvement of carcass quality in Nellore cattle. The variance components were estimated using the restricted maximum likelihood method for the thoracic perimeter (TP), frame size score (FRAME), yearling weight (YW), visual scores of body structure (BS), muscularity (MUSC), and precocity (PREC). The carcass traits included loin eye area (REA), backfat thickness (BF), rump fat (FR), and intramuscular fat (IF). The estimated heritabilities ranged from moderate to high. The FRAME showed a positive genetic correlation with YW (0.82 ± 0.07), TP (0.58 ± 0.09), and BS score (0.62 ± 0.07), but it had a negative correlation with the MUSC and PREC visual scores (- 0.34 ± 0.09 and - 0.50 ± 0.08, respectively). The genetic correlation between FRAME and REA was positive (0.26 ± 0.09). However, FRAME presented a correlation close to zero with BF, RF, and IF. TP had a positive genetic correlation with body size traits such as YW (0.76 ± 0.05) and BS score (0.55 ± 0.08) and with muscularity traits such as REA (0.44 ± 0.01). Frame size has the potential to be used as a parameter in the selection of precocious beef cattle, but a study of its use is necessary to determine the ideal biotype for each production system.