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Heterosis: Defined and Research Experience

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1 Heterosis: Defined and Research Experience
Scott P. Greiner, Ph.D. Extension Animal Scientist, Beef Department of Animal & Poultry Sciences Virginia Tech

2 Can We Have It All??? Reproductively efficient cow herd
Cows that are low-cost, adaptable to feed and environmental resources Superior growth/feed efficiency End product merit

3 Crossbreeding Fundamentals
Heterosis (Hybrid Vigor) Individual heterosis Maternal heterosis Paternal heterosis Breed complementarity

4 Heterosis Defined -Superiority of crossbred animal relative to average of its straightbred parents
Breed A Weaning Wt. = 530 lb. Breed B Weaning Wt. = 470 lb. A x B Crossbred Calf Expected performance 500 lb. (average of A and B) Actual performance = 520 lb. 20 lb. (4%) increase = heterosis

5 Genetic Basis of Heterosis
Additive vs. non-additive gene effects Additive: favorable effect on performance results from increase in homozygosity (heterozygote intermediate to homozygotes) Non-additive: favorable effects realized through increase in heterozygosity Dominance and epistasis

6 Dominance

7 Economically Important Traits
Reproductive efficiency Calving ease Calf survival Weaning Wt. Post-weaning growth Feed efficiency Mature size Red meat yield Palatability

8 Individual Heterosis Advantage of the Crossbred Calf
Cundiff and Gregory, 1999

9 Carcass Traits Long, 1980

10 Maternal Heterosis Cundiff and Gregory, 1999

11 Impact of Heterosis Heritability Low Moderate High Heterosis High Low
Reproduction Growth Carcass Merit

12 Maternal Heterosis Advantage of the Crossbred Cow
Advantage of crossbred cow vs. straightbred Reproductive efficiency Maternal ability Longevity Increased lifetime productivity Maternal heterosis accounts for largest portion of total heterosis advantage (60%)

13 Estimating Heterosis Expected Performance = General purebred mean
+ ½ sire breed direct value + ½ dam breed direct value + dam breed maternal value + individual heterosis + maternal heterosis

14 Weaning Weight Example
General mean = 600 Individual heterosis = 4.0% Maternal heterosis = 4.0%

15 Sire C x crossbred A-B dam
Calculated performance with direct and maternal breed values (40)+ 0.25(20) (-10) + 0.5(10) + 0.5(30) = 642.5 Add individual heterosis (642.5) = 668.2 Add maternal heterosis (668.2) = 694.9

16 Paternal Heterosis Advantage of the Crossbred Sire
Advantage in reproductive traits Realized primarily when single sires mated to high numbers of cows (> 40) Difficult to measure due to large influence of female in total herd reproductive efficiency

17 Breed Differences Sire breed of calf Gestation length, d Unassisted
calvings, % Birth weight, lb. Survival to wean., 200-d wean. wt., Hereford 284 95.6 90.4 96.2 524 Angus 282 99.6 84.0 96.7 533 Red Angus 99.1 84.5 526 Simmental 285 97.7 92.2 553 Gelbvieh 97.8 88.7 97.1 534 Limousin 286 97.6 89.5 96.9 519 Charolais 283 92.8 93.7 540 source: Cundiff et al., 2001, Germplasm Evaluation Program Progress Report No. 21

18 Effect of breed type on level of heterosis
Cundiff and Gregory, 1999

19 Heterosis: Bottom Line
Heterosis offers best genetic solution for improvement of lowly heritable reproductive traits Majority of heterosis advantages realized through crossbred dams

20 Considerations Breed contributions Optimizing heterosis
Heterosis retention Interaction with environment Economics of crossbreeding Sustainable systems to capture heterosis

21 Heterosis: Defined and Research Experience
Scott P. Greiner, Ph.D. Extension Animal Scientist, Beef Department of Animal & Poultry Sciences Virginia Tech

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