The possibility of in vivo carcass trait prediction using the ultrasound measurements obtained between 12 th and 13 th ribs was studied. Attention was paid to several carcass traits such as carcass backfat thickness (CBFT), carcass longissimus dorsi muscle (CLMA) and carcass weight (HCW). Also, the effects of the flock, as the fixed effects, and body weight (BW), as covariate, on these traits were considered. The study was carried out on 99 lamb of Torki-Ghashghaii breed from 4 flocks. BW had

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... gnificant effects (P< 0.001) on HCW, Fat-tail, CBFT, and CLMA, but had no significant effect on carcass longissimus dorsi muscle depth (CLMD) and width (CLMW). The flock had a significant effect (P< 0.0001) on HCW and CBFT, only. The correlations between ultrasound and carcass measurements, before and after adjustment for flock effect, ranged between (0.27 to 0.80) and (0.22 to 0.78), respectively. Estimates of CBFT, CLMW, CLMD and CLMA based on the corresponding ultrasound measurements explained 49%, 29%, 59%, and 64% of their variation, respectively. BW explained 57% variation of HCW and only 12% variation of Fat-tail. The introduction of two or three ultrasound measurements by stepwise procedure in the multiple regression equations improved the explanation of variation for all traits by 0.01 up to 0.13. The results indicate that ultrasound has potential for carcass traits prediction in live Torki-Ghashghaii sheep.