Selection for Increased Leanness of Yorkshire Swine. IV. Indirect Responses of the Carcass, Breeding Efficiency and Preweaning Litter Traits

Abstract

Indirect responses of carcass, breeding efficiency and preweaning litter traits resulting from direct selection for indices that measured percentage lean cuts at 81.6 kg live weight (PCLC line) and weight of lean cuts at 160 d of age (LG line) were evaluated. Indirect responses were measured by a least-squares weighted regression analysis that adjusted for generation environmental effects and compared selected lines to a control. In the PCLC line, the percentage of lean cuts increased by .63 ± .12%/ generation over the control (P<.01). Longissimus muscle area increased (P<.01) by .48 ±.11 cm²/generation and average backfat decreased (P<.01) by .10 ± .02 cm/generation. Few significant changes were noted in the quality characteristics in the PCLC line. Moisture content of longissimus muscle decreased by .10 ± .03%/generation (P<.01), subjective ham color decreased by .06 ± .02 points/generation (P<.01) and ether extract increased by .06 ± .03%/generation (P<.05). In the LG line, carcasses increased in length by .66 ± .10 cm/generation (P<.01). Longissimus depth decreased by .08 ± .02 cm/generation (P<.01), while width increased by .04 ± .01 cm/generation (P<.01). Quality traits within the LG line also changed little. Postmortem pH increased by .13 ± .06 units/generation (P<.05) and longissimus muscle ash decreased by .005 ± .002%/generation (P<.05). The breeding efficiency traits that measured discernible estrus, conception rate and farrowing rate were not different from the control in either selected line. The preweaning litter traits were not dramatically affected by selection for leanness in first parity litters. Second parity litters of the PCLC line, however, had fewer pigs than the control at every age, birth and d 1, 7 and 21. The LG line second parity litters had fewer pigs at d 1, 7 and 21. Copyright © 1983. American Society of Animal Science . Copyright 1983 by American Society of Animal Science.