Animal Science Departmental Report
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Genetic Correlations Between Growth and Carcass Traits
S. H. Oh, D. H. Lee1 and M. T. See
1Hakyong National University, Ansung, Korea
Pig breeding is currently accomplished with estimated breeding values (EBVs) or expected progeny differences (EPDs) to improve growth rate and backfat thickness. However, an optimum selection strategy would be improved with carcass and growth traits in balance. Therefore, it is important to investigate the relationship between growth and carcass traits to determine if undesirable genetic correlations exist between them. The objective of this study is to estimate genetic parameters of growth and carcass traits that are average daily gain (ADG), days to 90kg (DAY), backfat thickness (BF), eye muscle area (EMA) and dressing percentage (DP) in pigs.
Materials and Methods
Data were composed of average daily gain (ADG), days to 90kg (DAY), backfat thickness (BF), eye muscle area (EMA) and dressing percentage (DP) from 14,555 individuals at a farm in South Korea. Backfat thickness, EMA, and DP were measured with PIGlog 105 (SFK Technology)
The statistical model included year-season, breed, sex and parity as fixed effects, and the random genetic effect of animal. Test day and weight were included as covariates in the model. Test day is the period from individual birth date to test date. Data were analyzed with a multivariate animal model using software that used an EM-REML algorithm (REMLF90; Misztal, 2001) to obtain the (co)variance component estimates.
Results and Discussion
Results of analyses from the five-trait animal model for DAY, ADG, BF, EMA, and DP are given in Table 1. The estimate of heritability for days to 90kg in this study was 0.21 and was lower than previous studies. The estimate for ADG was 0.67 and consistent with average literature estimate of 0.62 by Hutchens et al. (1981).
For backfat, the estimate of this study was 0.44, and in the range of previous studies. Genetic parameters for EMA and DP in pigs have not been as extensively published in the literature as growth traits, but Sellier (1998) reviewed two studies and reported heritabilities as 0.47 and 0.30 for loin muscle area, and 0.48 and 0.36 for DP, respectively. In this study, the estimate of heritability for EMA and DP were 0.24 and 0.45, respectively. Therefore, genetic improvement through carcass traits would be possible enough from the estimates of heritability in carcass traits.
Genetic and phenotypic correlations among growth and carcass traits are also given in Table 1. Days to 90kg were estimated to have low negative genetic and favorable correlations with ADG of -0.07 and -0.64, respectively. It was also estimated to have low genetic correlations with BF, EMA and DP of 0.03, -0.02 and -0.07, respectively, and low phenotypic correlations with those of 0.13, 0.17 and 0.01, respectively. The estimate of genetic correlation between DAY and ADG differed greatly with that reported by Lubritz et al. (1991). Estimates of genetic correlation between days to 100kg and backfat have been reported -0.13 on average with four different breeds (Li and Kennedy, 1994) Chen et al. (2002) reported that genetic correlation estimates of days to 113.5kg with backfat and loin eye area adjusted to 113.5kg did not differ from zero.
Genetic and phenotypic correlations between ADG and BF are generally very low (Stanislaw et al., 1967; Li and Kennedy, 1994). The result in this study was in close agreement with those reports. However, Bereskin and Davey (1978) estimated phenotypic correlation of ADG and BF as 0.59, and McPhee et al. (1979) reported that genetic and phenotypic correlations as 0.55 and 0.10, respectively. Genetic correlation estimate between ADG and EMA was -0.10. Between EMA and BF, moderately unfavorable genetic correlation was estimated, and this finding is confirmed by Chen et al. (2002).
Dressing percentage had no genetic and phenotypic relationship with growth traits, but showed highly negative genetic and phenotypic correlations with BF and moderately positive genetic and phenotypic correlations. Few genotypic correlations related to dressing percentage have been previously reported in pigs. Sellier (1998) reviewed genetic correlations between ultrasonic BF and DP, and loin muscle area and DP. These estimates werereported as 0.18 and 0.50, respectively. From the results of this study, growth rate was not related to DP genetically, however, including carcass traits in selection program would be desirable to improve carcass components because the estimate of carcass traits was not that low.
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ADG = Average daily gain; DAY = Days to 90kg; BF = Backfat thickness; EMA= Eye muscle area; DP = Dressing percent