Genetic parameters and responses of performance and body composition traits in pigs selected for high and low growth rate on a fixed ration over a set time

Abstract

-Two lines of Large White pigs of common genetic origin were divergently selected over four years for high and low growth rate during a 6 week post-weaning test period in which all pigs were fed the same total amount of food (80% of estimated ad libitum intake). Genetic parameters and direct and correlated responses in performance and carcass traits were estimated on 2884 pigs with pedigrees comprising a total of 5324 animals, with restricted maximum likelihood and best linear unbiased prediction methods applied to a multi-trait animal model. Estimates of heritability (±SE) were 0.19 ± 0.04 for lifetime daily gain (LDG), 0.16 ± 0.03 for test daily gain (TDG), 0.25 ± 0.04 for ultrasound P2 backfat (UBF) and 0.16 ± 0.03 for food conversion ratio during test (TFC), and 0.15 ± 0.04 for daily carcass weight gain (CDG), 0.43 ± 0.06 for carcass backfat (CFT) and 0.40 ± 0.06 for carcass lean percentage (LEAN). Common litter effects for TDG, UBF and TFC were less than 5% and for LDG, 17% of total phenotypic variance. Genetic correlations between performance and carcass traits were moderately to highly favourable. After four years of divergent selection for growth rate, the selection responses in estimated breeding value (EBV) for TDG were 40.14 and -41.11 g (SED 2.95) for the high and low growth lines, respectively. The regressions of EBV on year of birth, indicate that the annual genetic trend for TDG, was 8.73 g/yr in the high and -8.48 g/yr in the low lines (P < 0.001). Correlated genetic responses in the high and low lines respectively were 5.28 g and -12.40 g (SED 2.09) in LDG, -0.35 mm and 0.56 mm (SED 0.009) in UBF, -0.145 units and 0.185 units (SED 0.012) in TFC, 3.17 g and -10.97 g (SED 1.53) in CDG, -1.13 mm and 1.01 mm (SED 0.155) in CFT and 1.24% and -1.27% (SED 0.150) in LEAN. It was concluded that selection for increased post-weaning daily gain on a ration of fixed amount reduces the age at slaughter and the level of backfat and increases the efficiency of food utilisation, weight and leanness of pig carcasses. divergent selection / pig / growth / restricted feeding / genetic responses

Genetic relationships and expected responses for genetic improvement of carcass traits of Berkshire pigs

“…The strong genetic correlation of BFTF with SCFB, SCFS, SCFH, and SCF10 was markedly favorable for genetic improvement of carcass traits and consistent with 0.85 reported by Lo et al (1992) and 0.81 by Nguyen and McPhee (2005), suggesting that back fat measured by US is prospectively conducive for the improvement of back fat thickness on carcasses in this Berkshire population. Nevertheless, because of the low genetic correlation between LEAF and LEAC (0.20), loin eye area measured by US was not effective in improving loin eye area in carcasses.…”

Genetic relationship between growth and carcass traits in Large White pigs

“…Most of the phenotypic variation for AREA is under genetic control; hence its improvement by direct selection is possible. The heritability estimate for CFAT (0.42 ± 0.08) is similar to the estimates obtained by Nguyen & McPhee (2005) and Gilbert et al (2007). Carcass fat is seldom measured in pigs because of the difficulty of assessing this trait in a large population and the ease with which backfat thickness can be measured.…”

“…The estimated heritability for AGES was 0.37 ± 0.04, which was slightly higher than the estimates reported by Li & Kennedy (1994) for three Canadian breeds. Feed conversion ratio had a heritability estimate of 0.24 ± 0.03, which is higher than the 0.16 ± 0.03 observed by Nguyen & McPhee (2005). These moderate heritability estimates indicate the existence of substantial genetic variation in this population, which may result in genetic improvement if direct selection is applied on the traits.…”

“…TPG had a lower heritability estimate (0.28 ± 0.03) compared with LTG (0.34 ± 0.05). Although Nguyen & McPhee (2005) obtained lower estimates for these traits (0.16 ± 0.03 and 0.19 ± 0.04, respectively) in Australian Large White pigs, they observed the same trend where test period gain is less heritable than lifetime gain. This is probably because more treatments were applied to the pigs during the test period.…”

“…The genetic correlations between BFAT and other growth traits were favourable, suggesting that selecting for reduced BFAT may improve growth performance and feed utilization, and may result in reduced slaughter age. A higher estimate was obtained by Nguyen & McPhee (2005) between backfat thickness and test period FCR (0.43 ± 0.13). Lo et al (1992) reported an unfavourable genetic correlation of -0.13 ± 0.12 between backfat thickness and age at 103.6 kg in US Duroc pigs.…”