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Estimates of genetic parameters and response to 10 generations of selection for residual feed intake in Yorkshire pigs
Objectives were to estimate response to 10 generations (G) of divergent selection for residual feed intake (RFI = observed feed intake - expected feed intake) in Yorkshire pigs and to estimate genetic parameters for growth performance traits. The low RFI (LRFI) line was selected for decreased EBV for RFI during grow-finish. The high RFI (HRFI) line was randomly selected until G4 and then selected for increased EBV for RFI from G5 to G10. Both lines were maintained with ~50 litters by ~12 boars, avoiding full- and half-sib matings with ~70 gilts per generation, except ~10 boars and ~40 gilts that produced ~30 litters in the first 4 generations of the HRFI line. Records analyzed were for pigs with off-test BW greater than 102 kg (n = 2,224). ASREML was used to estimate variance components, EBV, and responses to selection. The mixed model for analysis of ADFI, ADG, and feed conversion ratio (FCR = ADFI/ADG) included the fixed effects of pen within contemporary group, sex, and a covariate of on-test age, and random effects of additive genetic, litter and residual. The model for ultrasound traits of backfat (BF), loin muscle area (LMA) also included off-test BW as a covariate. Estimates for RFI were based on analysis of ADFI with additional covariates of on-age, on-test BW, off-test BW, ADG, BF, and average metabolic BW. Responses to selection based on EBV were compared to results from separate phenotype-based analyses of each generation using the MIXED procedure of SAS and to genetic trends obtained from separate genetic analyses by line. Estimates of heritability of RFI, ADFI, ADG, BF, LMA, and FCR were 0.28 ± 0.05, 0.45 ± 0.05, 0.38 ± 0.05, 0.49 ± 0.06, 0.53 ± 0.06, and 0.29 ± 0.05, respectively. Estimates of genetic correlations of RFI with ADFI, ADG, BF, LMA, and FCR were 0.69 ± 0.07, 0.16 ± 0.13, 0.23 ± 0.12, -0.32 ± 0.11 and 0.68 ± 0.08, respectively. After 9 generations of selection, the LRFI line had 201.4 g/d lower RFI (3.0 genetic SD), 276.9 g/d lower ADFI (2.1 SD), 29.1 g/d lower ADG (0.5 SD), 2.29 mm lower BF (0.82 SD), 1.48 cm² greater LMA (0.43 SD) and 0.26 g/g lower FCR (1.88 SD) than the HRFI line. In conclusion, feed efficiency based on RFI is moderately heritable and responds to selection. This work was supported by USDA-NIFA-AFRI-2011-68004-30336.
Keywords: pig, residual feed intake, selection