Genetic associations between carcass traits measured by real-time ultrasound and scrotal circumference and growth traits in Nelore cattle1

The aim of the present study was to evaluate the genetic correlations among real-time ul- trasound carcass, BW, and scrotal circumference (SC) traits in Nelore cattle. Carcass traits, measured by real- time ultrasound of the live animal, were recorded from 2002 to 2004 on 10 farms across 6 Brazilian states on 2,590 males and females ranging in age from 450 to 599 d. Ultrasound records of LM area (LMA) and backfat thickness (BF) were obtained from cross-sectional im- ages between the 12th and 13th ribs, and rump fat thickness (RF) was measured between the hook and pin bones over the junction between gluteus medius and bi- ceps femoris muscles. Also, BW (n = 22,778) and SC (n = 5,695) were recorded on animals born between 1998 and 2003. The BW traits were 120, 210, 365, 450, and 550-d standardized BW (W120, W210, W365, W450, and W550), plus BW (WS) and hip height (HH) on the ultrasound scanning date. The SC traits were 365-, 450-, and 550-d standardized SC (SC365, SC450, and SC550). For the BW and SC traits, the database used was from the Nelore Breeding Program—Nelore Bra- zil. The genetic parameters were estimated with mul- tivariate animal models and REML. Estimated genetic correlations between LMA and other traits were 0.06 (BF), −0.04 (RF), 0.05 (HH), 0.58 (WS), 0.53 (W120), 0.62 (W210), 0.67 (W365), 0.64 (W450 and W550), 0.28 (SC365), 0.24 (SC450), and 0.00 (SC550). Esti- mated genetic correlations between BF and with other traits were 0.74 (RF), −0.32 (HH), 0.19 (WS), −0.03 (W120), −0.10 (W210), 0.04 (W365), 0.01 (W450), 0.06 (W550), 0.17 (SC365 and SC450), and −0.19 (SC550). Estimated genetic correlations between RF and other traits were −0.41 (HH), −0.09 (WS), −0.13 (W120), −0.09 (W210), −0.01 (W365), 0.02 (W450), 0.03 (W550), 0.05 (SC365), 0.11 (SC450), and −0.18 (SC550). These estimates indicate that selection for carcass traits measured by real-time ultrasound should not cause antagonism in the genetic improvement of SC and BW traits. Also, selection to increase HH might de- crease subcutaneous fat as correlated response. There- fore, to obtain animals suited to specific tropical pro- duction systems, carcass, BW, and SC traits should be considered in selection programs.