Genetic effects on maternal, growth and carcass traits of swine
Three stress genotypes; homozygous normal (NN), heterozygous stress carrier (Nn), and homozygous stress positive (nn), were produced from Nn Duroc boars and Nn Minzhu sows. The NN piglets grew faster than the other two genotypes with an average 42 day litter weaning weight of 10.73 kg for the NN group, 9.47 kg for the Nn group, and 9.30 kg for the nn group and pre-weaning average daily gains of 0.227, 0.199, and 0.194 kg day-1, respectively. NN pigs required significantly fewer days to reach 105 kg exceeding the Nn pigs by 10.63 days and the nn pigs by 21.55 days. (P <.05). The nn group had larger longissimus muscle area (36.91 cm2) than both the Nn (35.08 cm2) and the NN group (32.91 cm2). Marbling score decreased with the number(s) of copies of the stress genes while firmness score moved in the opposite direction. Duroc pigs had 0.25 kg heavier average piglet birth weight and 9.20 mm less carcass backfat than the Minzhu backcrosses. The two groups, however, did not differ significantly in meat quality traits. In a second study, comparisons of litter, growth, carcass, and meat quality traits among three synthetic lines; high lean gain (HL), low lean gain (LL), and control (CL), produced from Meishan sows mated to Yorkshire boars were made. The HL possessed heavier average piglet 42 day weight, less backfat thickness, larger longissimus muscle areas, and higher lean percentages than the other two groups. There were no significant differences among the three synthetic lines for meat quality traits except muscle pH (P <.05). Comparisons between the Yorkshire-Meishan combination (YM) and purebred Yorkshires (YY) were also made for these traits. YM were higher in number of piglets born per litter (12.75 vs. 12.14 pigs), lower in litter birth weight (16.28 vs. 18.74 kg), shorter in carcass length (79.56 vs. 83.26 cm), higher in backfat thickness (37.50 vs. 25.79 cm), smaller in longissimus muscle area (26.04 vs. 39.20 cm2), and lower in lean percentage (42.26 vs. 47.98%) than the YY. The crossbreds, however, had higher longissimus muscle color (3.27 vs. 2.94), marbling (3.23 vs. 2.31), and firmness scores (3.27 vs. 2.72) than the YY. All of the differences between the two groups for carcass and meat quality traits were significant (P <.05). Estimations of genetic parameters for litter and growth traits by the Multiple Trait Derivative-Free Restricted Maximum Likelihood (MTDFREML) procedure were made from Landrace, Yorkshire, and Duroc populations. Estimates of heritability (h2) for number piglets born alive per litter were 0.02, 0.11, and 0.02 in Landrace, Yorkshire, and Duroc, respectively. The average h2 estimates of average daily gain (LADG), backfat thickness (ALBF10), longissimus muscle area (ALLMA), days to 105 kg (LD105), lean percentage (LP), live pig daily lean gain (LADLGT) and live pig body length (LBL) were 0.70, 0.50, 0.54, 0.65, 0.71, 0.52, and 0.44, respectively. The genetic correlations between LADLGT and LADG, and between LADLGT and LD105 were 0.69 and -0.92, respectively.