Effect of Using Ultrasonic Muscle Depth and Fat Depth on the Accuracy of Predicted Phenotypic and Genetic Values of Carcass Traits on Live Ram Lambs

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Abstract
Ultrasonic scanning was used to measure muscle depth and fat depth at the third lumbar vertebra of 556 ram lambs of the Norwegian Dala and Spælsau breeds in three ram circles in 1990. After slaughter, carcass weight, carcass grade, muscling score, fat score and weight of kidney and kidney fat were recorded. The increase in accuracy of predicting carcass weight and grade by including ultrasonic measurements in addition to weaning weight was low, whereas a considerable increase in accuracy of fat score was observed for Dala. A genetic analysis of 355 recorded progeny sired by 44 young Dala rams was made. Estimates of heritabilities from the REML procedure were: 0.46 ± 0.22 for muscle depth and 0.26 ± 0.17 for fat depth. Genetic correlations were estimated. The accuracy of the selection indexes for carcass weight, carcass grade or fat score increased significantly when ultrasonic measures were added compared to use of weaning weight and sire records only.