applied beef cattle breeding and selection inbreeding and heterosis in beef cattle larry v. cundiff...

Applied Beef Cattle Breeding and Selection

Inbreeding and Heterosis in Beef Cattle

Larry V. CundiffARS-USDA-U.S. Meat Animal Research Center

2008 Beef Cattle Production Management Series-Module IVGreat Plains Veterinary Education Center

University of Nebraska, Clay CenterAugust 1, 2008

Homework

Participants Module 2 Module 3

Anderson

Castleberry

Davidson X X

Fox X

Frese X

Furman X X

Jones X X

Langon

Linhart X X

Matlick X X

Van Boening X X

Werhman

Ondrack X X

Email homework to

[email protected]

Fullsib

Firstcousin

Outbreeding

within abreed

SelfFertili-zation

Halfsib

RandomMatingIn a purebreed

Crossbreeding

Speciescrosses

Degrees of inbreeding according to relationship of mates(Lush, 1945)

Zygotic Frequency with Self Fertilzation of a Heterozygote (Aa)

Female

gamete

Male gamete

.5 A .5 a

.5 A .25 AA .25 Aa

.5 a .25 Aa .25 aa

Change in genotypic frequency with self fertilization

Generation AA Aa aa

0 100

1 25 50 25

2 37.5 25 37.5

3 43.75 12.5 43.75

4 46.875 6.25 46.875

5 48.4375 3.125 43.75

… … … …Various

but many50 0 50

-0.2

0

0.2

0.4

0.6

0.8

1

AAAaaa

No Dominance (additive)

Partialdominance

Effects of different degrees of dominance on phenotypic value

Complete dominance

?

Homo-Zygousline

InbredLineF = .5

SireDaughter

OrFull sib

PureBreed

Randommated

Crossbreeding

?

100

80

60

40

20

0

0

20

40

60

80

100

HOMOZYGOSITY

(%)

AAOraa

HETEROZYGOSITY

(%)

Aa

Effects of inbreeding on heterozygosity/homozygosity(Cundiff and Gregory, 1977)

Average expected performance of crossbred, purebred, and inbred lines with additive and

non additive gene effects.

Frequency (%) per /genotype Addi-tive

Partal

Dom.

Com-plete

Dom.AA Aa aa

Crossbred 0 100 0 0.5 0.75 1.0Purebred 10 80 10 0.5 0.70 0.9Sire-daughter 20 60 20 0.5 0.65 0.8Inbred line F=.5 30 40 30 0.5 0.60 0.7Homozygous line 50 0 50 0.5 0.50 0.50

Effects of inbreeding in cattle (Brinks et al., 1975. Western Regional Project W-1, Tech. Bulletin 123)

• Fertility (percentage of cows pregnant declined 2% and 1.3% with each 10% increase in inbreeding of the dam and calf, respectively.

• Percentage calf crop weaned declined 1.6% and 1.1% with each 10 percent inbreeding of the dam and calf, respectively.

• Inbreeding also depressed growth and maternal weaning weight.

Sire breed Dam breed Calf breed Weaning wt

H A HA 430

A H AH 416

A A AA 405

H H HH 395

HA = 430 = .5gH + .5 gA + hIha + mA

AH = 416 = .5gH + .5 gA + hIha + mH

AA = 405 = gA + + mA

HH = 395 = gH + + mH

(.5)(HA + AH) + .5 (AA + HH) = 423 – 400 = 23 = hIah

Estimating Heterosis for a specific two breed cross

C X A = .5gC + .5 gA + hIca + mA

C X B = .5gC + .5 gB + hICB + mB

C X AB = .5gC + .25 gA + .25gB + .5hIAC + .5hI

BC + .5mA + .5 mB + hM

AB

C X BA = .5gC + .25 gB + .25gA + .5hIAC + .5hI

BC + .5mA + .5 mB + hM

AB

.5[( C X AB) + (C X BA)] – .5[(C X A) + (C X B)] = hMAB

Estimating Maternal Heterosis

HETEROSIS EFFECTS IN CROSSES OF HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUSBOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUSBOS INDICUS X BOS TAURUS BREEDS BREEDS

FROM DIALLEL CROSSING EXPERIMENTSFROM DIALLEL CROSSING EXPERIMENTS

Bos taurus XBos taurus X Bos indicus XBos indicus X No. Bos taurus No. Bos taurus No. Bos taurus No. Bos taurusTraitTrait Est. Units %Est. Units % Est. Units % Est. Units %

Crossbred calves (individual heterosis)Crossbred calves (individual heterosis)

Calving rate, %Calving rate, % 1111 3.23.2 4.44.4Survival to weaning, %Survival to weaning, % 1616 1.41.4 1.91.9Birth weight, kgBirth weight, kg 1616 .8.8 2.42.4 44 3.33.3

11.111.1Weaning weight, kgWeaning weight, kg 1616 7.37.3 3.93.9 1010 21.721.7

12.612.6Postweaning ADG, g/dPostweaning ADG, g/d 1919 3434 2.62.6 66 116116

16.216.2Yearling weight, kgYearling weight, kg 2727 13.213.2 3.83.8Cutability, %Cutability, % 2424 -.3-.3 -.6-.6Quality grade, 1/3 gr.Quality grade, 1/3 gr. 2424 .12.12 ------ 66 .3.3

------

HETEROSIS EFFECTS IN CROSSES OF HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUSBOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUSBOS INDICUS X BOS TAURUS BREEDS BREEDS

FROM DIALLEL CROSSING EXPERIMENTSFROM DIALLEL CROSSING EXPERIMENTS

Bos taurus XBos taurus X Bos indicus XBos indicus X No. Bos taurus No. Bos taurus No. Bos taurus No. Bos taurusTraitTrait Est. Units %Est. Units % Est. Units % Est. Units %

Crossbred cows (maternal heterosis)Crossbred cows (maternal heterosis)

Calving rate, %Calving rate, % 1313 3.53.5 3.73.7 77 9.99.913.413.4

Survival to weaningSurvival to weaning 1313 .8.8 1.51.5 77 4.74.75.15.1

Birth weight, kgBirth weight, kg 1313 .7.7 1.81.8 66 1.91.95.85.8

Weaning weight, kgWeaning weight, kg 1313 8.28.2 3.93.9 1212 31.131.116.016.0

Longevity, yrsLongevity, yrs 33 1.361.36 16.216.2

Lifetime prod.Lifetime prod. No. CalvesNo. Calves 33 .97.97 17.017.0 Cum. wn. wt., kgCum. wn. wt., kg 33 272272 25.325.3

Weight of Calf Weaned Per Cow Weight of Calf Weaned Per Cow Exposed To BreedingExposed To Breeding

8.58.5

14.814.8

8.58.5

23.323.3

Straightbredcows

straightbredcalves

Straightbredcows

X-bredcalves

X-bredcows

X-bredcalves

Per

cen

t

•Heterosis increases Heterosis increases production per cow 20 to 25% production per cow 20 to 25% in in Bos taurus x Bos taurus Bos taurus x Bos taurus crosses and at leastcrosses and at least 50% in 50% in Bos indicus x Bos taurus Bos indicus x Bos taurus crosses in subtropical crosses in subtropical regions.regions.

•More than half of this effect More than half of this effect is dependent on use of is dependent on use of crossbred cows.crossbred cows.

HeterosisHeterosis

LONGEVITY AND LIFETIME PRODUCTION OFLONGEVITY AND LIFETIME PRODUCTION OFSTRAIGHTBRED HEREFORD (H), ANGUS (A), HEREFORD XSTRAIGHTBRED HEREFORD (H), ANGUS (A), HEREFORD X

ANGUS (HA) AND ANGUS X HEREFORD (AH) COWSANGUS (HA) AND ANGUS X HEREFORD (AH) COWS

Breed groupTrait H A HA AH Heterosis

Longevity, yrs. 8.4 9.4 11.0 10.6 1.9* Lifetime production No. calves 5.9 6.6 7.6 7.6 1.3* Wt of calves weaned, lb. 2405 2837 3259 3515 766*

*P < .05

• Heterosis Effects are greatest for lowly heritable traits:Reproduction SurvivalLongevity

• Heterosis effects are moderate for moderately heritable traits:

Direct and maternal weaning weightPostweaning gain

• Heterosis effects are small for highly heritable traits:Feed efficiencyCarcass traits

Retail product %Fat thickness

Marbling

ConclusionsConclusions

Static Three-breed Cross SystemStatic Three-breed Cross System

Offspring marketedPounds of calf/cowincreased about19%

45-50%of

Cows

25-30%of

Cows

25%of

Cows

A B C

A A AB

Rotational Crossbreeding Rotational Crossbreeding SystemsSystems

Two breedTwo breed Three breedThree breedrotationrotation rotationrotation

Heterosis for Production Per Cow in Hereford, Heterosis for Production Per Cow in Hereford, Angus, and Shorthorn Rotational CrossesAngus, and Shorthorn Rotational Crosses

First GenerationFirst GenerationObserved (%)Observed (%) 1616 2424Expected (%)Expected (%)aa 1919 2323

Second GenerationSecond GenerationObserved (%)Observed (%) 2424 3535Expected (%)Expected (%)aa 1414 2121

aaBased on individual and maternal heterosis observed Based on individual and maternal heterosis observed in F1 generation and assumes that retained heterosis in F1 generation and assumes that retained heterosis is proportional to retained heterozygosityis proportional to retained heterozygosity..

Genetic Composition and Heterosis ExpectedGenetic Composition and Heterosis Expectedin a Two-Breed Rotationin a Two-Breed Rotation

Heteroz. of Est. Heteroz. of Est. Additive geneticAdditive genetic progenyprogeny in wt. in wt. comp. of progenycomp. of progeny relative to F1 relative to F1 wnd/cowwnd/cowaa

SireSire AA BBGenerationGeneration breedbreed %% %% % % %%

11 AA 5050 5050 100100 8.58.522 BB 2525 7575 5050 19.019.033 AA 6363 3737 7575 13.813.844 BB 3131 6969 6363 16.416.455 AA 6666 3434 6969 15.215.266 BB 3333 6767 6666 15.815.877 AA 6767 3333 6767 15.515.5

aaBased on heterosis effects of 8.5% for individual traits and 14.8% for Based on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits, when loss of heterosis in proportional to loss of maternal traits, when loss of heterosis in proportional to loss of

heterozygosityheterozygosity

Genetic Composition and Heterosis Expected in aGenetic Composition and Heterosis Expected in aThree-Breed RotationThree-Breed Rotation

Additive GeneticAdditive Genetic Heteroz. of Est. increase Heteroz. of Est. increase Comp. of Progeny progeny in wt.Comp. of Progeny progeny in wt.

SireSire A B C A B C relative to F1relative to F1 wnd/cowwnd/cowaa GenerationGeneration breedbreed % % % %% % % % % %

11 AA 5050 0 0 50 50 100 100 8.58.522 BB 2525 5050 25 25 100100 23.323.333 CC 1212 2525 6262 7575 21.221.244 AA 5656 1212 3131 8888 18.618.655 BB 2828 5656 1616 8888 20.520.566 CC 1414 2828 5858 8484 20.220.277 AA 5757 1414 2929 8686 19.719.788 BB 2929 5757 1414 8686 20.020.0

aaBased on heterosis effects of 8.5% for individual traits and 14.8% for maternal Based on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits when loss of heterosis is prportional to loss of heterozygosity.traits when loss of heterosis is prportional to loss of heterozygosity.

Rotational Crossbreeding Rotational Crossbreeding SystemsSystems

Rotational crossing systemsRotational crossing systems maintain heterosis maintain heterosis

proportional to heterozygosityproportional to heterozygosity

Next time : Composite Populationsand alternative crossbreeding systems.

MARC I¼ Limousin, ¼

Charolais,¼ Brown Swiss,

c Angus and c Hereford

Limousin

Charolais

Angus Hereford

Brown Swiss (Braunvieh)

MARC II ¼ Simmental, ¼ Gelbvieh,¼ Hereford and ¼ Angus

Angus

Simmental

Gelbvieh

Hereford

MARC III ¼ Pinzgauer, ¼ Red Poll,¼ Hereford and ¼ Angus

Pinzgauer

Red Poll

Angus

Hereford

HETEROSIS EFFECTS AND RETAINED HETEROSISIN COMPOSITE POPULATIONS VERSUS CONTRIBUTING

PUREBREDS (Gregory et al., 1992)

Composites minus purebredsComposites minus purebreds

TraitTrait F F11 F F22 F F3&43&4

Birth wt., lbBirth wt., lb 3.63.6 5.05.0

5.1 5.1

200 d wn. wt., lb200 d wn. wt., lb 42.442.4 33.433.4

33.733.7

365 d wt., females, lb365 d wt., females, lb 57.357.3 51.451.4

52.052.0

365 d wt., males, lb365 d wt., males, lb 63.563.5 58.658.6

59.859.8

Age at puberty, females, dAge at puberty, females, d -21-21 -18-18

-17-17

Scrotal circumference, inScrotal circumference, in .51.51 .35.35

.43.43

200 d weaning wt., (mat.), lb200 d weaning wt., (mat.), lb 3333 3636

Calf crop born, (mat.), %Calf crop born, (mat.), % 5.45.4 1.71.7

Calf crop wnd., (mat.), %Calf crop wnd., (mat.), % 6.36.3 2.12.1

200 d wn. wt./cow exp. (mat.), lb200 d wn. wt./cow exp. (mat.), lb 5555 3737

Composite populations Composite populations maintain heterosismaintain heterosis

proportional to heterozygosityproportional to heterozygosity

(n-1)/n or 1 – (n-1)/n or 1 – P Pii22

Rotational crossing systemsRotational crossing systems or or

composite populations composite populations

maintain significant heterosismaintain significant heterosis

MODEL FOR HETEROZYGOSITY IN A TWO BREED COMPOSITE

Breed Breed of sireDam ½ A ½ B

½ A ¼ AA ¼ AB½ B ¼ BA ¼ BB

(n-1)/n or 1 – (n-1)/n or 1 – P Pii2 2 = .50= .50

MODEL FOR HETEROZYGOSITY IN A THREE BREED COMPOSITE

Breed Breed of sireDam .50 A .25 B .25 C

.50 A .25 AA .125 BA .125 CA

.25 B .125 BA .0625 BB .0625 CB

.25 C .125 AC .125 BC .0625 CC

1 – 1 – P Pii2 2 = (1 - = (1 - .375.375) = .625) = .625

Weaning Wt Marketed Per Cow Exposed for Alternative Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%)Crossbreeding Systems Relative to Straightbreeding (%)

Straight breeding 0 0 0

2-breed rotation (A,B) .67 .67 15.53-breed rotation (A,B,C) .86 .86 20.04-breed rotation (A,B,C,D) .93 .93 21.7

2-breed composite (5/8 A, 3/8 B) .47 .47 11.02-breed composite (.5 A, .5 B) .5 .5 11.73-breed composite (.5A, .25 B, .25C) .625 .625 14.64 breed composite (.25A,.25B,.25C,.25D) .75 .75 17.5

F1 bull rotation (3-breed: AB, AC) .67 .67 15.5F1 bull rotation (4-breed: AB, CD) .83 .83 19.3

Wean. wt H i Hm marketed System (+ 8.5%) (+14.8%) per cow exp

Composite populationsComposite populations provide for provide for effective use ofeffective use of

• HeterosisHeterosis• Breed differencesBreed differences• Uniformity and end product Uniformity and end product

consistencyconsistency

Genetic Variation in Alternative Mating SystemsGenetic Variation in Alternative Mating Systems

OptimumOptimum

Assumes that the Two FAssumes that the Two F11’s Used are of Similar Genetic Merit’s Used are of Similar Genetic Merit

Genetic potential for USDA Quality Grade and USDA

Yield Grade is more precisely optimized in cattle

with 50:50 ratios of Continental to British breed

inheritance.

COMPLEMENTARITY

is maximized in terminal crossing systems

Cow HerdSmall to moderate sizeAdapted to climateOptimal milk production

for feed resources

Terminal Sire BreedRapid and efficient growthOptimizes carcass composition

and meat quality in slaughter progeny

ProgenyMaximize high quality lean beefproduced per unit feed consumedby progeny and cow herd

Rotational and Terminal Sire Rotational and Terminal Sire Crossbreeding ProgramsCrossbreeding Programs

Cow

Age No.

1 20 2 18 3 15

2 Breed Rotation

A B

4 13 5 12 - - - - 12 1

T x (A-B) T x (A-B)

Lbs. Calf/Cow 21% 18%

45%

55%

1/2A - 1/2B

Two Breed Composite


Straight breeding 0 0 0 0

2-breed rotation (A,B) .67 .67 15.5 20.83-breed rotation (A,B,C) .86 .86 20.0 24.14-breed rotation (A,B,C,D) .93 .93 21.7 25.4

2-breed composite (5/8 A, 3/8 B) .47 .47 11.0 17.32-breed composite or F1 bulls (.5 A, .5 B) .5 .5 11.7 17.83-breed composite (.5A, .25 B, .25C) .625 .625 14.6 20.34 breed composite (.25A,.25B,.25C,.25D) .75 .75 17.5 22.2

F1 bull rotation (3-breed: AB, AC) .67 .67 15.5 20.8F1 bull rotation (4-breed: AB, CD) .83 .83 19.3 23.6

Wean. wt Terminal H i Hm marketed crossa

System + 8.5% +14.8% per cow exp (+5% wt/calf)

a Assumes 66 % of calves marketed (steers and heifers) are by terminal sire breed out of more mature age dams and 33% are by maternal breeds (steers only).

SUMMARYSUMMARY

Figure 6. Use of heterosis, additive breed effects andComplementarity with alternative crossbreeding systems.

• Similarity in mean performance of British and Continental European Similarity in mean performance of British and Continental European breeds means they are more suited for use in rotational cross-breeds means they are more suited for use in rotational cross-breeding systems today than 30 years agobreeding systems today than 30 years ago

• Performance levels are not expected to fluctuate as much with Performance levels are not expected to fluctuate as much with rotational crossing for growth traits and cow size . Growth rate can rotational crossing for growth traits and cow size . Growth rate can be stabilized by using Across-breed EPDs. be stabilized by using Across-breed EPDs.

• Differences in birth weight are still significant and warrant use of Differences in birth weight are still significant and warrant use of sire breeds with lighter birth weight on first calf heifers (i.e., Angus, sire breeds with lighter birth weight on first calf heifers (i.e., Angus, Red Angus, etc.).Red Angus, etc.).

• Intergeneration fluctuations in milk production still persist but they Intergeneration fluctuations in milk production still persist but they are less than half as great as 30 years ago. Milk levels can be are less than half as great as 30 years ago. Milk levels can be stabilized by using Across-breed EPDs.stabilized by using Across-breed EPDs.

Implications for Crossbreeding

• Advantages of terminal sire crossing systems are not as great Advantages of terminal sire crossing systems are not as great today as 30 years ago due to similarity of breeds for rate and today as 30 years ago due to similarity of breeds for rate and efficiency of growth. efficiency of growth.

• However, differences between British and Continental breeds in However, differences between British and Continental breeds in carcass traits are still significant and relatively large.carcass traits are still significant and relatively large.

• Inter generation fluctuations in mean performance for carcass Inter generation fluctuations in mean performance for carcass traits are still large and significant. traits are still large and significant.

• For carcass traits, uniformity and end-product consistency can For carcass traits, uniformity and end-product consistency can still be enhanced by use of composite populations or hybrid bulls.still be enhanced by use of composite populations or hybrid bulls.

• Adaptation to intermediate subtropical/temperate environments Adaptation to intermediate subtropical/temperate environments can be optimized with greater precision by use of composite can be optimized with greater precision by use of composite populations or hybrid bulls. populations or hybrid bulls.

Implications for Crossbreeding

Heterosis proportional to heterozygosity in various matings

Pure breed 0 0Two breed F1 cross (A x B) 100 0 F2 (AB x AB) 50 100 F3 (AB x AB) (or F4, ..Fn) = 2 breed Composite 50 50 Backcross (A x AB) 50 100 1st backcross interse (A-AB x A-AB) 37.5 50 ¾-1/4 composite (.75A, .25B) 37.5 37.5 5/8-3/8 composite (.625 A, .375 B) 47 47 2 breed rotation 67 67

Three way cross (A x BC) 100 100 1st 3-way interse (A - BC) x (A-BC) 62.5 100 3 –breed composite (.5 A, .25 B, .25C) 62.5 62.5 3 breed rotation (A, B, C) 86 86 Rotation F1 hybrids, 1 common breed (AB -AC) 67 67

Four way cross 100 100 4- breed composite (.25 A, .25B, .25C, .25 D) 75 75 4-breed rotation (A, B, C, D) 93 93 Rotation 2 F1 hybrids (AB - CD) 83 83

Mating type Progeny Dam

Rotational and Terminal Sire Rotational and Terminal Sire Crossbreeding ProgramsCrossbreeding Programs

Cow

Age No.

1 20 2 18 3 15

2 Breed Rotation

A B

3 Breed Rotation

B

A C

4 13 5 12 - - - - 12 1

T x (A-B) T x (A-B-C)

Lbs. Calf/Cow 21% 24%

45%

55%

Cross breeding of composite populations can be used to Cross breeding of composite populations can be used to exploit: exploit:

• HETEROSISHETEROSIS

• COMPLEMENTARITY among breeds optimize COMPLEMENTARITY among breeds optimize performance levels for important traits and to match performance levels for important traits and to match genetic potential with:genetic potential with:

Market preferencesMarket preferencesFeed resourcesFeed resourcesClimatic environmentClimatic environment

BREED DIFFERENCES an important genetic resource

CEFFICIENTS OF VARIATION IN PUREBRED AND COMPOSITE POPULATIONS (Gregory et al., 1992)

TraitTrait Purebreds Composites Purebreds Composites

Gestation length, dGestation length, d .01.01

.01.01

Birth wt. Birth wt. .11.11

.12 .12

200 d wn. wt.200 d wn. wt. .09.09

.09.09

365 d wt., females365 d wt., females .08 .08

.08.08

365 d wt., males365 d wt., males .09.09

.09.09

Age at puberty (females)Age at puberty (females) .08 .08

.07.07

Scrotal circumferenceScrotal circumference .07.07

.07.07

5 yr cow wt, lb5 yr cow wt, lb .07.07

.08.08

5 yr height, in5 yr height, in .02.02

.02.02

Steer carcass wt, lbSteer carcass wt, lb .08.08

.08.08

Rib-eye areaRib-eye area .10.10

.10.10

Retail product, %Retail product, % .04.04

.06.06

Retail product, lbRetail product, lb .19.19

.20.20

COMPLEMENTARITY

is maximized in terminal crossing systems

Cow HerdSmall to moderate sizeAdapted to climateOptimal milk production

for feed resources

Terminal Sire BreedRapid and efficient growthOptimizes carcass composition

and meat quality in slaughter progeny

ProgenyMaximize high quality lean beefproduced per unit feed consumedby progeny and cow herd

General Considerations

• Rotational SystemsRotational Systems

Provide for more effective use of Provide for more effective use of • HeterosisHeterosis

• Composite populationsComposite populations

Provide for more effective use of Provide for more effective use of • Breed differencesBreed differences• Uniformity and end product consistencyUniformity and end product consistency

Effect of Heterosis on Percentage Cows Remaining in HerdEffect of Heterosis on Percentage Cows Remaining in HerdAt Different Ages Relative to Those Originally RetainedAt Different Ages Relative to Those Originally Retained

as Breeding Heifersas Breeding Heifers

Crossbred cows

Straightbred cows

Pe

rce

nta

ge

Co

ws

Re

ma

inin

gP

erc

en

tag

e C

ow

s R

em

ain

ing

Age At Exposure to Breeding (years)Age At Exposure to Breeding (years)

Rotational Crossbreeding ProgramsRotational Crossbreeding Programs

A B

3 Breed2 Breed

C

A B

Increase Lbs. CalfPer Cow 15%

Increase Lbs. CalfPer Cow 19%

Genetic Variation in Alternative Mating SystemsGenetic Variation in Alternative Mating Systems

OptimumOptimum

Assumes that the Two FAssumes that the Two F11’s Used are of Similar Genetic Merit’s Used are of Similar Genetic Merit


Straight breeding 0 0 0 0

2-breed rotation (A,B) .67 .67 15.5 20.83-breed rotation (A,B,C) .86 .86 20.0 24.14-breed rotation (A,B,C,D) .93 .93 21.7 25.4

2-breed composite (5/8 A, 3/8 B) .47 .47 11.0 17.32-breed composite or F1 bulls (.5 A, .5 B) .5 .5 11.7 17.83-breed composite (.5A, .25 B, .25C) .625 .625 14.6 20.34 breed composite (.25A,.25B,.25C,.25D) .75 .75 17.5 22.2

F1 bull rotation (3-breed: AB, AC) .67 .67 15.5 20.8F1 bull rotation (4-breed: AB, CD) .83 .83 19.3 23.6

Wean. wt Terminal H i Hm marketed crossa

System + 8.5% +14.8% per cow exp (+5% wt/calf)

a Assumes 66 % of calves marketed (steers and heifers) are by terminal sire breed out of more mature age dams and 33% are by maternal breeds (steers only).

applied beef cattle breeding and selection inbreeding and heterosis in beef cattle larry v. cundiff...

Documents