Heterosis: Defined and Heterosis: Defined and

Research ExperienceResearch Experience

Scott P. Greiner, Ph.D.

Extension Animal Scientist, Beef

Department of Animal & Poultry Sciences

Virginia Tech

sgreiner@vt.edu

Can We Have It All???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

Crossbreeding FundamentalsCrossbreeding Fundamentals

Heterosis (Hybrid Vigor)– Individual heterosis– Maternal heterosis– Paternal heterosis

Breed complementarity

Heterosis DefinedHeterosis Defined--Superiority of crossbred animal relative to average Superiority of crossbred animal relative to average of its straightbred parentsof its straightbred parentsBreed 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

Genetic Basis of HeterosisGenetic Basis of Heterosis Additive vs. non-additive gene effectsAdditive: 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

DominanceDominance

0

10

20

30

40

50

60

No dominance(additive)

Partial dominance Complete dominance

AA Aa aa

Economically Important TraitsEconomically Important Traits

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

Individual HeterosisIndividual HeterosisAdvantage of the Crossbred CalfAdvantage of the Crossbred Calf

Trait Units %Calving rate, % 3.2 4.4Survival to weaning, % 1.4 1.9Birth weight, lb. 1.7 2.4Weaning weight, lb. 16.3 3.9ADG, lb./d .08 2.6Yearling Wt. 29.1 3.8

Cundiff and Gregory, 1999Cundiff and Gregory, 1999

Carcass TraitsCarcass Traits

Trait heterosis Dressing percent 0 REA 3% Fat thickness 5% Quality grade 1% Cutability 1%

Long, 1980Long, 1980

Maternal HeterosisMaternal HeterosisTrait Units % Calving rate, % 3.5 3.7 Survival to weaning, % .8 1.5 Birth weight, lb. 1.6 1.8 Weaning weight, lb. 18.0 3.9 Longevity, yr. 1.36 16.2 Lifetime Production No. Calves .97 17.0 Cumulative Wean. Wt. 600 25.3 Cundiff and Gregory, 1999Cundiff and Gregory, 1999

Impact of HeterosisImpact of Heterosis

Reproduction

Growth

Carcass Merit

Heritability

Low

Moderate

High

Heterosis

High

High

Low

Maternal HeterosisMaternal HeterosisAdvantage of the Crossbred CowAdvantage 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%)

Estimating HeterosisEstimating Heterosis

Expected Performance =General purebred mean

+ ½ sire breed direct value

+ ½ dam breed direct value

+ dam breed maternal value

+ individual heterosis

+ maternal heterosis

Weaning Weight ExampleWeaning Weight Example

Direct Value lb.

Maternal Value lb.

Breed A +20 +10 Breed B -10 +30 Breed C +40 -50

General mean = 600 Individual heterosis = 4.0% Maternal heterosis = 4.0%

Calculated performance with direct and maternal breed values600 + 0.5(40)+ 0.25(20) + 0.25(-10) + 0.5(10) + 0.5(30) = 642.5

Add individual heterosis642.5 + 0.04(642.5) = 668.2

Add maternal heterosis668.2 + 0.04(668.2) = 694.9

Sire C x crossbred A-B damSire C x crossbred A-B dam

Paternal HeterosisPaternal HeterosisAdvantage of the Crossbred SireAdvantage 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

Breed DifferencesBreed DifferencesSire breedof calf

Gestationlength,

d

Unassistedcalvings,

%

Birthweight,

lb.

Survivalto wean.,

%

200-dwean. wt.,

lb.

Hereford 284 95.6 90.4 96.2 524

Angus 282 99.6 84.0 96.7 533

Red Angus 282 99.1 84.5 96.7 526

Simmental 285 97.7 92.2 96.7 553

Gelbvieh 284 97.8 88.7 97.1 534

Limousin 286 97.6 89.5 96.9 519

Charolais 283 92.8 93.7 97.1 540

source: Cundiff et al., 2001, Germplasm Evaluation Program Progress Report No. 21

Effect of breed typeEffect of breed type on level of heterosis on level of heterosis

Bos taurus x Bos taurus

Bos indicus x Bos taurus

Individual heterosis Birth weight 2.4 11.1 Weaning weight 3.9 12.6 ADG 2.6 16.2 Maternal heterosis Calving rate 3.7 13.4 Calf survival 1.5 5.1 Birth weight 1.8 5.8 Weaning weight 3.9 16.0

Cundiff and Gregory, 1999Cundiff and Gregory, 1999

Heterosis: Bottom LineHeterosis: Bottom Line

Heterosis offers best genetic solution for improvement of lowly heritable reproductive traits

Majority of heterosis advantages realized through crossbred dams

ConsiderationsConsiderations

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

heterosis

Heterosis: Defined and Heterosis: Defined and

Research ExperienceResearch Experience

Scott P. Greiner, Ph.D.

Extension Animal Scientist, Beef

Department of Animal & Poultry Sciences

Virginia Tech

sgreiner@vt.edu