By means of the application of covariance models, the linear effects of the proportion of Duroc genes were evaluated with respect to growth (from 6 to 170 kg live weight) and feed/gain ratios, as well as carcass (lean cuts, adipose cuts, linear measures, backfat thickness, loin area and lean percentage) and meat quality (L* a* b* colour, reflectance, electrical conductivity, pH) in 167 heavy pigs (87 castrated males, 80 females) from different crosses of Duroc (D), Large White (LW) and Landrace (L) breeds, from 25 to approximately 300 d of age. The pigs were weighed at 25, 105, 170, 235 d and at the end of the trial (298 ± 6 d of age), and were raised under the same conditions. The proportion of Duroc genes was 0% (LWxL; no. 33), 25% [(LWx(DxL); n. 31 and Lx(DxLW); n. 35)] and 50% [Dx(LWx(LWxL)); n. 68]. The increase in the proportion of Duroc genes negatively affected the live weight at the different ages (P<0.05), but the weight at slaughtering was not affected (P>0.10). In fact, during the final phase (from 120 to 170 kg l.w.) the effect of the Duroc breed on daily gain became positive (P=0.08), and the feed/gain ratios were significantly lower (P=0.02). The carcass composition was not significantly influenced by the increase in the proportion of Duroc genes, with the exception of a rise in the weight of neck (P<0.01) and flare fat (P=0.02) and a reduction of ham (P=0.09). Carcass length resulted lower as the proportion of Duroc genes increased (P<0.01); at 24 h from slaughtering, meat colour showed lower values for lightness (P=0.08), redness (P=0.02) and yellowness (P=0.03).
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