Heterosis – The Forgotten Tool?Heterosis – The Forgotten Tool?

Dr. Tom FieldDr. Tom Field

Colorado State UniversityColorado State University

Dr. Andy HerringDr. Andy Herring

Texas A&M UniversityTexas A&M University

Cattlemen’s CollegeCattlemen’s College2005 NCBA Meeting, San Antonio2005 NCBA Meeting, San Antonio

General CommentsGeneral Comments

The seedstock cattle industry exists as a The seedstock cattle industry exists as a business only because of the demands business only because of the demands of the commercial cattle industry.of the commercial cattle industry.

Without purebred animals, FWithout purebred animals, F11 crossbred crossbred

animals cannot be produced.animals cannot be produced.

Basics of Quantitative Genetics

Performance = Genetics + EnvironmentPerformance = Genetics + Environment

Genetic aspects are:Genetic aspects are:1. Additive (breeding value – gene content)1. Additive (breeding value – gene content)2. Non-additive (hybrid vigor – gene 2. Non-additive (hybrid vigor – gene combinations) combinations)

Alleles at a gene locus can act additively (or not).Alleles at a gene locus can act additively (or not).Genotypes across gene loci can act additively (or not).Genotypes across gene loci can act additively (or not).

Breeding SystemsBreeding Systems

• It is important to know breed It is important to know breed characteristics to fully take advantage characteristics to fully take advantage of breeding systems of breeding systems

• It is important to know characteristics It is important to know characteristics of different types of breeding systems of different types of breeding systems

Properly designed beef cattle Properly designed beef cattle crossbreeding programs have the crossbreeding programs have the potential of substantially potential of substantially improving production efficiency improving production efficiency over commercial straightbreeding over commercial straightbreeding programs. programs.

The improved efficiency from The improved efficiency from crossbreeding can result from:crossbreeding can result from:

1.1. Heterosis (hybrid vigor) Heterosis (hybrid vigor)

2.2. Blending, in the offspring, of Blending, in the offspring, of characteristics from different breeds characteristics from different breeds and/or,and/or,

3.3. Characteristics of the dams and sires as Characteristics of the dams and sires as these characteristics, themselves, affect these characteristics, themselves, affect the efficiency of the system. the efficiency of the system.

HeterosisHeterosis

Hybrid vigor (also called heterosis) is the Hybrid vigor (also called heterosis) is the higher performance of crossbred animals as higher performance of crossbred animals as compared to purebred animals.compared to purebred animals.

For a particular pair of breeds, the hybrid For a particular pair of breeds, the hybrid vigor for a particular character is the vigor for a particular character is the average amount that the average of the Faverage amount that the average of the F11 exceeds the average of the two pure breeds. exceeds the average of the two pure breeds.

HeterosisHeterosisExampleExample: Weaning weight information: Weaning weight information

Brahman average = 500 lbBrahman average = 500 lbHereford average = 460 lb Hereford average = 460 lb B x H average = 516 lbB x H average = 516 lbH x B average = 540 lbH x B average = 540 lb

HV =((516 + 540)/2) - ((500 +460)/2) = 528 - 480HV =((516 + 540)/2) - ((500 +460)/2) = 528 - 480 = 48 lb= 48 lb = 48/480 = 10% = 48/480 = 10%

HeterosisHeterosis

--most important for reproduction and survival traitsmost important for reproduction and survival traits -tends to be higher between breeds that are more -tends to be higher between breeds that are more

genetically different from each other (2 to 3 times higher genetically different from each other (2 to 3 times higher in in Bos indicus/Bos taurusBos indicus/Bos taurus crosses than in crosses than in Bos taurus/Bos Bos taurus/Bos taurustaurus crosses) crosses)

-highest in F-highest in F11, and tends to be proportional to degree of , and tends to be proportional to degree of heterozygosityheterozygosity

-especially important for female productivity (reproduction -especially important for female productivity (reproduction and maternal ability)and maternal ability)

Crossbred CowsCrossbred Cows

Because of heterosis for female Because of heterosis for female productivity (fertility, calf weaning productivity (fertility, calf weaning weight, longevity), much of the weight, longevity), much of the advantage from crossbreeding systems advantage from crossbreeding systems comes from the use of crossbred cow.comes from the use of crossbred cow.

Maternally Influence CharactersMaternally Influence Characters

Performance for a maternally influenced Performance for a maternally influenced character (such as weaning weight) is a character (such as weaning weight) is a function offunction of

1. breed composition of the calf1. breed composition of the calf2. heterosis in the calf (direct)2. heterosis in the calf (direct)3. breed composition of the dam 3. breed composition of the dam 4. heterosis in the dam (maternal)4. heterosis in the dam (maternal)

How to Estimate HeterosisHow to Estimate Heterosis

There are two major considerations here:There are two major considerations here:

1.1. The actual amount of increased performance The actual amount of increased performance in units of the trait in Fin units of the trait in F11 animals. animals.

2.2. The expected fraction (or percentage) of the The expected fraction (or percentage) of the FF11 advantage in other types of crosses. advantage in other types of crosses.

How to Estimate HeterosisHow to Estimate Heterosis

FF11 animals will exhibit 100% heterosis between animals will exhibit 100% heterosis between

the two breeds involved, but this is 100% of the two breeds involved, but this is 100% of some actual advantage in performance.some actual advantage in performance.

For example:For example:In some FIn some F11 crosses, this may be 100% of a 25 lb crosses, this may be 100% of a 25 lb

advantage, and in other Fadvantage, and in other F11 crosses this may crosses this may

be 100% of a 40 lb advantage.be 100% of a 40 lb advantage.

How to Estimate Percent HeterosisHow to Estimate Percent Heterosis

Heterosis percent (fraction) is based on the Heterosis percent (fraction) is based on the fraction of gene loci in animals that are fraction of gene loci in animals that are expected to have two alleles from two expected to have two alleles from two different breeds.different breeds.

Angus bulls x Hereford cows => FAngus bulls x Hereford cows => F11 calves calves

These calves are ½ Angus, ½ Hereford, but These calves are ½ Angus, ½ Hereford, but 100% of their gene loci are heterozygous.100% of their gene loci are heterozygous.

How to Estimate Percent HeterosisHow to Estimate Percent Heterosis

If we take FIf we take F11 bulls and F bulls and F11 heifers and mate them: heifers and mate them:

FF11 bulls (½ A ½ H) x F bulls (½ A ½ H) x F11 heifers (½ A ½ H) heifers (½ A ½ H)

=> F=> F22 calves (½ A ½ H) calves (½ A ½ H)

The FThe F22 calves are expected to have ½ heterosis calves are expected to have ½ heterosis

themselves (50% direct), but also benefit from themselves (50% direct), but also benefit from heterosis in cows (100% maternal).heterosis in cows (100% maternal).

How to Estimate Percent HeterosisHow to Estimate Percent Heterosis

If you know the fractions of the breeds in the parents, If you know the fractions of the breeds in the parents, you can estimate the fraction of heterosis in you can estimate the fraction of heterosis in progeny (based on chance of inheritance).progeny (based on chance of inheritance).

½ A ½ H bulls x ½ A ½ Gelbvieh cows½ A ½ H bulls x ½ A ½ Gelbvieh cows=> ½ A ¼ H ¼ G calves=> ½ A ¼ H ¼ G calves

Heterosis in calves can come from A-G, H-G, H-A Heterosis in calves can come from A-G, H-G, H-A combinations, each has ¼ chance of occurrence.combinations, each has ¼ chance of occurrence.

We would say these calves have 75% heterosis. We would say these calves have 75% heterosis.

HeterosisHeterosis• Heterosis increases production per cow Heterosis increases production per cow

20 to 25% in 20 to 25% in Bos taurus x Bos taurus Bos taurus x Bos taurus crosses and at leastcrosses and at least 50% in Bos indicus x 50% in Bos indicus x Bos taurus Bos taurus crosses in subtropical regions.crosses in subtropical regions.

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

Cumulative Effects Of Heterosis For WeightCumulative Effects Of Heterosis For WeightOf Calf Weaned Per Cow Exposed To BreedingOf Calf Weaned Per Cow Exposed 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 Utilization is Critical for Heterosis Utilization is Critical for Commercial ProducersCommercial Producers

Consider pounds of calf weaned per cow exposed to breedingConsider pounds of calf weaned per cow exposed to breeding

Cow-calf SystemCow-calf System Productivity* lb calf Productivity* lb calf

1.1. Straightbred cows producing Straightbred cows producing straightbred calvesstraightbred calves 100100 450 450

2. Straightbred cows producing2. Straightbred cows producingcrossbred calvescrossbred calves 108.5 488108.5 488

3.3. Crossbred cows producingCrossbred cows producing crossbred calvescrossbred calves 123.3 555123.3 555

*Based on data from USDA MARC involving *Based on data from USDA MARC involving Bos taurusBos taurus crosses and purebreds. crosses and purebreds.

Heterosis Depends on Crossbreeding System and Breeds

Type of system Example Direct MaternalTerminal F1 crossCharolais x Hereford 100 0Terminal F1 crossBrahman x Hereford 200 0Two breed rotation Angus, Hereford 67 67Two breed rotation Angus, Brahman 133 133Three breed terminal Charolais x F1 Angus-Hereford 100 100Three breed terminal Charolais x F1 Brahman-Hereford 150 200Three breed rotation Angus, Simmental, Gelbvieh 86 86Three breed rotation Angus, Brahman, Charolais 143* 143*Two breed composite 50% Hereford, 50% Simmental 50 50

50% Angus, 50% Brahman100 1005/8 Charolais, 3/8 Red Angus 47 475/8 Shorthorn, 3/8 Brahman 84 84

Four Breed Composite 25% each A, H, S, C 75 7525% A, Br, C, G 112.5 112.525% A, Br, L, Nellore 125 125

*Some crosses in the system will exhibit more heterosis than others.

Average birth weights at the McGregor Station 1992-1997Average birth weights at the McGregor Station 1992-1997______________________________________________________________________________________________________________  

Birth Weight (lb)Birth Weight (lb)Sire breedSire breed Dam breedDam breed bulls bulls heifersheifers average average______________________________________________________________________________________________________________  HerefordHereford Hereford Hereford 80 80 76 76 78 78  BrahmanBrahman Brahman Brahman 74 74 71 71 72.5 72.5  HerefordHereford Brahman Brahman 75 75 73 73 74 74  BrahmanBrahman Hereford Hereford 101 101 87 87 94 94____________________________________________________________________________________________________________

Crossbreeding SystemsCrossbreeding Systems

A real challenge in beef cattle A real challenge in beef cattle breeding is to develop effective, breeding is to develop effective, sustainablesustainable crossbreeding systems. crossbreeding systems.

1. It should be possible for all the breeding stock that are 1. It should be possible for all the breeding stock that are needed for the system to be produced in the same needed for the system to be produced in the same region where the system will be operated.region where the system will be operated.

2. The system should be fairly simple to operate. 2. The system should be fairly simple to operate. 3. All cattle used in and produced by the system should be 3. All cattle used in and produced by the system should be

adapted to the local environment.adapted to the local environment.4. There should be no major incompatibilities between the 4. There should be no major incompatibilities between the

cattle that are mated.cattle that are mated.5. All animals that are produced in the system must be 5. All animals that are produced in the system must be

acceptable to local market conditions.acceptable to local market conditions.

In order for a crossbreeding system to be sustainable In order for a crossbreeding system to be sustainable in a region, it should have the following in a region, it should have the following

characteristics:characteristics:

Example of Three Breed Composite

Composite that is ½ Angus, ¼ Charolais, and ¼ Composite that is ½ Angus, ¼ Charolais, and ¼ HerefordHereford

1/2A 1/4C 1/4H bulls x 1/2A 1/4C 1/4H cows 1/2A 1/4C 1/4H bulls x 1/2A 1/4C 1/4H cows

=> 1/2A 1/4C 1/4H calves=> 1/2A 1/4C 1/4H calves

Breed combinations in calves can be:Breed combinations in calves can be:

A-C, A-H, or C-H.A-C, A-H, or C-H.

Breed CombinationsBreed Combinations in Calves

¼ A-A¼ A-A 1/8 A-C1/8 A-C 1/8 A-H1/8 A-H

1/8 C-A1/8 C-A 1/16 C-C1/16 C-C 1/16 C-H1/16 C-H

1/8 H-A1/8 H-A 1/16 H-C1/16 H-C 1/16 H-H1/16 H-H

CowsCows ½ A ½ A ¼ C ¼ C 1/4H 1/4H

BullsBulls ½ A½ A

¼ C¼ C

¼ H¼ H

Heterosis in calves = 1/8 +1/8 + 1/8 + 1/8 + 1/16 + 1/16Heterosis in calves = 1/8 +1/8 + 1/8 + 1/8 + 1/16 + 1/16 = 5/8 or 62.5%= 5/8 or 62.5%

Results From Research ProjectsResults From Research Projects

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 3518 3514 766*

*P < .05

TAMU Diallele ProjectTAMU Diallele Project

• Purebred and FPurebred and F11 cows of Angus, Hereford, cows of Angus, Hereford, Brahman, Holstein and Jersey were Brahman, Holstein and Jersey were evaluated over a 14 year period.evaluated over a 14 year period.

• Only production reason for culling was if Only production reason for culling was if cow failed to give birth to live calf every 24 cow failed to give birth to live calf every 24 months, or if cow appeared unable to raise months, or if cow appeared unable to raise another calf.another calf.

Breed typeBreed type Percent remainingPercent remaining Productive life (yr)Productive life (yr)

AngusAngus 77 10.310.3

BrahmanBrahman 1717 9.79.7

HerefordHereford 55 9.89.8

HolsteinHolstein 00 7.37.3

JerseyJersey 00 6.26.2

Angus-BrahmanAngus-Brahman 3838 14.714.7

Angus-HerefordAngus-Hereford 2222 11.711.7

Angus-HolsteinAngus-Holstein 1414 12.312.3

Angus-JerseyAngus-Jersey 88 9.99.9

Brahman-HerefordBrahman-Hereford 3838 13.213.2

Brahman-HolsteinBrahman-Holstein 4141 13.613.6

Brahman-JerseyBrahman-Jersey 2222 11.811.8

Hereford-HolsteinHereford-Holstein 1818 11.811.8

Hereford-JerseyHereford-Jersey 2020 12.012.0

Holstein-JerseyHolstein-Jersey 00 8.88.8

Research Project in NebraskaResearch Project in Nebraska

Angus, Hereford and Shorthorn evaluated as purebred Angus, Hereford and Shorthorn evaluated as purebred and as Fand as F11 crossbred cows for cow productivity and crossbred cows for cow productivity and

longevity.longevity.

Cows born 1960-1963 and were kept until they were 12 Cows born 1960-1963 and were kept until they were 12 to 15 years old.to 15 years old.

Survival percentage to 12 yr and Survival percentage to 12 yr and longevity (kept to 12-15 yr old)longevity (kept to 12-15 yr old)

Breed typeBreed type Survival (%)Survival (%) Longevity (yr)Longevity (yr)

HerefordHereford 19.819.8 8.58.5

AngusAngus 43.543.5 9.49.4

ShorthornShorthorn 13.013.0 7.37.3

Hereford-AngusHereford-Angus 46.346.3 10.810.8

Hereford-ShorthornHereford-Shorthorn 34.934.9 8.88.8

Angus-ShorthornAngus-Shorthorn 45.345.3 9.69.6

Mouth scores based on teeth length Mouth scores based on teeth length in aged cowsin aged cows

Breed typeBreed type Mouth scoreMouth score

HerefordHereford 11.011.0

AngusAngus 11.811.8

ShorthornShorthorn 10.310.3

Hereford-AngusHereford-Angus 15.115.1

Hereford-ShorthornHereford-Shorthorn 16.516.5

Angus-ShorthornAngus-Shorthorn 13.813.8

Higher number indicates more tooth remaining.

Reasons for Nebraska cows culledReasons for Nebraska cows culled

TAMU Riesel ProjectTAMU Riesel Project

• Production of FProduction of F11 calves in 1982-1985 by calves in 1982-1985 by

mating Angus, Gray Brahman, Gir, Indu-mating Angus, Gray Brahman, Gir, Indu-Brazil, Nellore and Red Brahman sires to Brazil, Nellore and Red Brahman sires to Hereford cows.Hereford cows.

• All cows were kept to measure productivity All cows were kept to measure productivity and longevity.and longevity.

• Udder, teat and teeth soundness evaluatedUdder, teat and teeth soundness evaluated

Comparison of FComparison of F11 Cows at McGregor, TX Cows at McGregor, TX

through 14 years of agethrough 14 years of age

% CC lb calf per% CC lb calf per % still % still Type of cowType of cow BWT BWT WWT weaned cow exposed in herd WWT weaned cow exposed in herd

Angus-HAngus-H 86.6 86.6 499 499 83.3 83.3 416416 53% 53%

Gray Brahman-HGray Brahman-H 81.6 81.6 566 566 88.4 88.4 500500 53% 53%

Gir-HGir-H 76.6 76.6 562 562 91.5 91.5 514514 73% 73%

Indu-Brazil-HIndu-Brazil-H 81.8 81.8 563 563 81.0 81.0 456456 33% 33%

Nellore-HNellore-H 81.1 81.1 566 566 96.1 96.1 544544 80% 80%

Red Brahman-HRed Brahman-H 81.9 81.9 574 574 86.0 86.0 494494 43% 43%

Comparison of FComparison of F11 Cows at McGregor, TX Cows at McGregor, TX

through 14 years of agethrough 14 years of age

Teats that were too large, and/or udders that were too Teats that were too large, and/or udders that were too pendulous caused increases in calf illness because it was pendulous caused increases in calf illness because it was difficult for calves to nurse on their own initially.difficult for calves to nurse on their own initially.

Size of udder did not appear related to milk production within a Size of udder did not appear related to milk production within a breed.breed.

Nellore crossbred cows had smallest teats and tighest udders, Nellore crossbred cows had smallest teats and tighest udders, and best overall production and longevity.and best overall production and longevity.

All of All of Bos indicus-Bos indicus-Hereford FHereford F11 cows had better mouths later in cows had better mouths later in

life than Angus-Hereford Flife than Angus-Hereford F11 cows. cows.

Heterosis Retention Project at Heterosis Retention Project at McGregor, TexasMcGregor, Texas

• Initiated in mid 1990s to measure heterosis Initiated in mid 1990s to measure heterosis retention in retention in Bos indicus-Bos taurusBos indicus-Bos taurus crosses. crosses.

• Purebred Angus, Hereford, Brahman and Purebred Angus, Hereford, Brahman and Nellore.Nellore.

• Cow reproduction and productivity major Cow reproduction and productivity major focus of project.focus of project.

Heterosis Retention Project - McGregor, TXHeterosis Retention Project - McGregor, TX

Heterosis estimates for individual traits.Heterosis estimates for individual traits.

%CCB%CCB %CCW%CCW WWTWWT lb calf/cowlb calf/cow

B/A FB/A F11 9.59.5 1111 29 lb (6.3%)29 lb (6.3%) 74 lb (23%)74 lb (23%)

B/H FB/H F11 1515 15.515.5 88 lb (20.7%)88 lb (20.7%) 146 lb (53%)146 lb (53%)

B/A FB/A F22 -6.5-6.5 -6.0-6.0 1 lb (0.2%)1 lb (0.2%) -30 lb (-9%)-30 lb (-9%)

B/H FB/H F22 1313 14.514.5 42 lb (9.9%)42 lb (9.9%) 103 lb (37%)103 lb (37%)

Heterosis May Vary Across Environments

• There have been several research projects in cattle where there seems to be more heterosis expressed in more challenging environments.

Matching GeneticMatching GeneticPotential to the Potential to the

Climatic EnvironmentClimatic Environment

(Olson et al., 1991)(Olson et al., 1991)

Note that important differences in Note that important differences in environments can be across the fence environments can be across the fence from each other.from each other.

SummarySummary

Because of heterosis for female Because of heterosis for female productivity (fertility, calf weaning productivity (fertility, calf weaning weight, longevity), much of the weight, longevity), much of the advantage from crossbreeding systems advantage from crossbreeding systems comes from the use of crossbred cow.comes from the use of crossbred cow.

Bad Breeding Decisions are Costly