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Genetic Parameters Revisited for Ultrasound Scanning Traits in Australian Sheep
Genetic parameters were estimated for ultrasound scanned fat (FAT) and eye muscle (EMD) depths in sheep from analyses including and excluding body weight (WT) as a covariate and derived equivalent genetic parameters post analysis. Direct heritability estimates from univariate analyses were all moderate (0.17 to 0.25). Estimates from models with WT adjusted were about 30% higher. From bivariate analyses of WT with EMD and FAT, genetic variance for WT adjusted for EMD and FAT was higher than derived estimates, with increased heritability estimates for WT and negative genetic correlations compared to both unadjusted estimates (positive) and derived estimates (weakly positive). Phenotypic adjustment of scanned eye muscle and fat depths to constant body weight could over-correct estimated breeding values for these traits and post analysis adjustment may be a better approach, allowing use of more appropriate models in genetic evaluation.
Keywords:
eye muscle depth
fat depth
body weight
