EFFECT OF SELECTION FOR CARCASS SCORE ON THE GENETIC IMPROVEMENT OF ITS COMPONENTS IN SWINE

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Abstract
Selection for carcass score was practiced for ten generations in two separate lines of Yorkshire pigs. Three components of the score were studied: carcass length, loin eye area, and backfat thickness. In line 2, carcass score was the sole criterion of selection, while in line 3, it was combined with feed utilization into an overall merit. Line 1, selected solely for feed utilization, served as a control. Carcass length and loin eye area increased by approximately 2 and 9%, respectively, in both lines. However, backfat thickness also increased by about 3% in line 2 and 0.4% in line 3. Pooled heritability estimates derived from the analysis of variance and the regression of offspring on mid-parent were 0.64 for carcass length, 0.48 for loin eye area and 0.67 for backfat thickness. Genetic correlations among the components of carcass score, between the components and carcass score and between the components and feed utilization were moderately high and favorable for combined genetic improvement of all traits.