1
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2
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- Crossbreeding and heterosis in an all-breed animal model
- Estimate breed differences routinely
- Recommend mating strategies
- Inbreeding depression adjustments in genetic evaluations
- Within-breed interactions predicted using dominance relationships
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3
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- Crossbred animals
- Will have EBVs, most did not before
- Reliable EBVs from both parents
- Purebred animals
- Information from crossbred relatives
- More contemporaries
- Routinely used in other populations
- New Zealand (1994), Netherlands (1997)
- USA goats (1989)
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4
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5
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- All-breed animal model
- Purebreds and crossbreds together
- Age adjust to 36 months, not mature
- Variance adjustments by breed
- Unknown parents grouped by breed
- Westell groups instead of regressing on breed fractions
- General heterosis subtracted
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6
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- Groups formed based on
- Birth year
- Breed
- Path (dams of cows, sires of cows, parents of bulls)
- Origin (domestic vs other countries)
- Paths have >1000 in last 15 years
- Groups each have >500 animals
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7
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8
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- Genetic base
- Compute on all-breed base
- Convert back to within-breed-of-sire bases for ease of comparing to
previous PTA
- Heterosis and inbreeding
- Both effects removed in the animal model
- Heterosis added to crossbred animal PTA
- Expected Future Inbreeding (EFI) and genetic merit differ with mate
breed
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9
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- Adjust for inbreeding depression
- Remove past F, include future F
- Expected future F (EFI) = .5 mean Aij
- EBV0 vs EBVEFI vs unadjusted EBV
- Optimal selection theory
- Maximize w’ EBV0 + by.F w’ A w
- Use of EBV0 avoids double-counting
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10
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- Protein genetic trend estimates
- 3% more for EBV0 than EBV
- 6% less for EBVEFI than EBV
- Correlations of EBVs within breed
- .993 corr(EBVEFI, EBV) for cows
- .998 corr(EBVEFI, EBV) for bulls
- Select on EBV0 for crossbreeding?
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11
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- Dominance relationship matrix
- 5.5 million Holstein cows with data
- 1.6 million interactions among 4263 sires and maternal grandsires
- 30 minutes for D-1, 16 hours to solve
- Dominance variance
- Assumed 5% of phenotypic variance
- Estimate from Van Tassell et al, 2000
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12
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13
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- Can predict genetic interactions
- Inbreeding adjustments since 2005
- All-breed animal model expected 2007
- Sire-MGS dominance effects within breed mostly smaller than heterosis
- Future research on interactions
- Specific heterosis and epistasis
- Delivery of information to breeders
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