Responses to 19 generations of litter size selection in the NE Index line. II. Growth and carcass responses estimated in pure line and crossbred litters.

Our objective was to estimate responses in growth and carcass traits in the NE Index line (I) that was selected for 19 generations for increased litter size. Differences between Line I and the randomly selected control line (C) were estimated in pure line litters and in F1 and three-way cross litters produced by mating I and C females with males of unrelated lines. Contrasts of means were used to estimate the genetic difference between I and C and interactions of line differences with mating type. In Exp 1, 694 gilts that were retained for breeding, including 538 I and C and 156 F1 gilts from I and C dams mated with Danbred NA Landrace (L) sires, were evaluated. Direct genetic effects of I and C did not differ for backfat (BF) at 88.2 kg or days to 88.2 kg; however, I pigs had 1.58 cm2 smaller LM area than did C pigs (P < 0.05). Averaged over crosses, F1 gilts had 0.34 cm less BF, 4.29 cm2 greater LM area, and 31 d less to 88.2 kg than did pure line gilts (P < 0.05). In Exp 2, barrows and gilts were individually penned for feed intake recording from 27 to 113 kg and slaughtered. A total of 43 I and C pigs, 77 F1 pigs produced from pure line females mated with either L or Danbred NA 3/4 Duroc, 1/4 Hampshire boars (T), and 76 three-way cross pigs produced from F1 females mated with T boars were used. Direct genetic effects of I and C did not differ for ADFI, ADG, G:F, days to 113 kg, BF, LM area, ultimate pH of the LM, LM Minolta L* score, or percentage of carcass lean. Interactions of line effects with crossing system were significant only for days to 113 kg. Pure line I pigs took 4.58+/-4.00 d more to reach 113 kg than did C pigs, whereas I cross F1 pigs reached 113 kg in 6.70+/-3.95 d less than C cross F1 pigs. Three-way cross and F1 pigs did not differ significantly for most traits, but the average crossbred pig consumed more feed (0.23+/-0.04 kg/d), gained more BW per unit of feed consumed (0.052+/-0.005 kg/kg), grew faster (0.20+/-0.016 kg/d), had less BF (-0.89+/-0.089 cm), greater LM area (5.74+/-0.926 cm2), more lean (6.21+/-0.90%), and higher L* score (5.27+/-1.377) than the average pure line pig did (P < 0.05). Nineteen generations of selection for increased litter size produced few correlated responses in growth and carcass traits, indicating these traits are largely genetically independent of litter size, ovulation rate, and embryonic survival.