Effectiveness of Reciprocal Selection for Performance of Crosses between Montana No. 1 and Yorkshire Swine III. Expected and Actual Response

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Abstract
Index selection for preweaning litter size, litter weight and postweaning growth of both purebred and reciprocal crossbred litters of Montana No. 1 (Ms) and Yorkshire (Ys) swine was compared with purebred selection in Montana No. 1 (Mc) from 1953 to 1967 at Miles City. Purebred selection of Ms and Ys in even years was similar to that applied every year in Mc, but only one-half of potential maximum; crossbred selection in odd years was essentially maximum. Selection applied was more intense than intended for numbers weaned and less than intended for postweaning gains of boar and gilt pigs and sire progenies. Estimated 10-year genetic changes (ΔG) were compared with those expected E(ΔG) from actual selection applied and the heritabilities and genetic correlations computed from associations among relatives in the same data. Full-sib heritability estimates ranged from 10 to 36% for litter size and litter weights at birth, 21 and 56 days as traits of sows; half-sib estimates were about 30% for 84-day postweaning gain of pigs and 50% for backfat probe. There were no significant genetic Full-sib heritability estimates ranged from 10 to 36% for litter size and litter weights at birth, 21 and 56 days as traits of sows; half-sib estimates were about 30% for 84-day postweaning gain of pigs and 50% for backfat probe. There were no significant genetic correlations of litter size with postweaning growth or backfat probe at 92 kg live weight or of postweaning gain with backfat probe, but faster litter postweaning gain was significantly associated genetically with shorter gestations (r = -.45) and with heavier birth (r = .42) and weaning weights (r = .77). Sire effects on progeny were significant and important for numbers of stillborn pigs and for preweaning and postweaning growth and backfat thickness. Maternal environmental effects were important for all measures of preweaning and postweaning growth but not for backfat probe. ΔG and E(ΔG) were similar for sow productivity of Ms Ys reciprocal crosses (1.9± 1.1 vs. 1.5 in pigs weaned, 50 ± 14 vs. 53 kg in litter weight weaned) and in Mc controls (0.5 ± .3 vs. 0.6 pigs and 23 ± 4 vs. 29 kg) but not in parental Ms (-2.7 ± 1.7 vs. 2.2 pigs and -30 ± 16 vs. 71 kg) or Ys (0.5 t 2.7 vs. 0.8 pigs and -24 ± 32 vs. 34 kg). At in weight gain from 56 to 140 days equaled or exceeded predictions in all lines and crosses (18 ± 2 vs. 13 kg in crosses, 17 t 2 vs. 10 kg in Mc, 26 ± 4 vs. 18 kg in Ms and 9 ±11 vs. 9 in Ys). Gestation length increased more than expected in all three lines (4.5 ±.3 days vs. -.5) and in crosses (2.0 ±.5 vs. -.5). Backfat increased most in Ms and Ys lines (4.6 ±2.4 mm vs. -.6) and decreased in crosses (-3.3 t 2.5 mm vs. -.6). Direct comparison of Ms -Ys and Mc -Ys crosses, as well as cumulative deviation of Ms and Ys lines and crosses from Mc controls, indicates that progeny test selection for litter size and growth of crossbred litters can be expected to improve growth rate of crosses and especially of parent lines at least as rapidly as selection for purebred performance, with some loss of litter size in parent lines but not in crossbred litters. Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.

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