Estimation of genetic associations between reproduction and production traits based on a sire and dam line with common ancestry
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Genetic parameters for survival, reproduction and production traits were estimated for a sire and dam line, originating from one Large White breed separated more than 25 years ago. The change in parameters due to different selection pressure on reproduction and production traits in both lines was also examined. Data collected between 1990 and 2007 were available for the analysis of reproduction traits in 4713 litters (sire line) and 14 836 litters (dam line) and for the production traits in 58 329 pigs (sire line) and 108 912 pigs (dam line). Genetic parameters were estimated using a Bayesian approach. Average phenotypic differences between lines were substantial with 1.5 more piglets born in the dam line and 1.7mm less backfat thickness (BF) in the sire line. Based on a multiple trait analysis which included both reproduction and production traits, heritabilities for survival and litter size traits in the sire (or dam) line were estimated at 0.0360.01 (0.0660.01) for percentage of stillborn piglets (SB), 0.1060.03 (0.1160.01) for total number of piglets born (NBT) and 0.0960.03 (0.0960.01) for number of piglets born alive. Heritabilities for production traits were estimated at 0.2960.01 (0.2960.01) for average daily gain, 0.5060.01 (0.4260.01) for BF and 0.4160.01 for muscle depth. Selection pressure on litter size in the dam line resulted in a slightly unfavourable correlation for SB–NBT (0.2160.11), which was only marginally unfavourable in the sire line (0.0660.24). Selection pressure on BF in the sire line may have resulted in the moderately undesirable correlation with SB (20.4660.15), which was not significant in the dam line (20.0860.06). Changing the base population in the dam line to animals born since the year 2000 indicated that selection pressure on different traits has altered the heritabilities and correlations of the traits within the line. The undesirable correlations between survival at birth and reproduction traits or production traits were low so that simultaneous improvement of all traits can be achieved. Heritabilities for survival at birth and reproduction traits were low, but genetic variation was substantial and extensive pedigree information can be used to improve the accuracy of breeding values, so that genetic improvement is expected to be efficient.
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