Heterosis

1
Heterosis The Forgotten Tool?

• Dr. Tom Field
• Colorado State University
• Dr. Andy Herring
• Texas AM University

Cattlemens College 2005 NCBA Meeting, San Antonio
2
General Comments

• The seedstock cattle industry exists as a
  business only because of the demands of the
  commercial cattle industry.
• Without purebred animals, F1 crossbred animals
  cannot be produced.

3
Basics of Quantitative Genetics

• Performance Genetics Environment
• Genetic aspects are
• 1. Additive (breeding value gene content)
• 2. Non-additive (hybrid vigor gene
  combinations)
• Alleles at a gene locus can act additively (or
  not).
• Genotypes across gene loci can act additively (or
  not).

4
Breeding Systems

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

5

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

6
The improved efficiency from crossbreeding can
result from

1. Heterosis (hybrid vigor)
2. Blending, in the offspring, of characteristics
   from different breeds and/or,
3. Characteristics of the dams and sires as these
   characteristics, themselves, affect the
   efficiency of the system.

7
Heterosis

• Hybrid vigor (also called heterosis) is the
  higher performance of crossbred animals as
  compared to purebred animals.
• For a particular pair of breeds, the hybrid
  vigor for a particular character is the average
  amount that the average of the F1 exceeds the
  average of the two pure breeds.

8
Heterosis

• Example Weaning weight information
• Brahman average 500 lb
• Hereford average 460 lb
• B x H average 516 lb
• H x B average 540 lb
• HV ((516 540)/2) - ((500 460)/2) 528 - 480
• 48 lb
• 48/480 10

9
Heterosis

• -most important for reproduction and survival
  traits
• -tends to be higher between breeds that are more
  genetically different from each other (2 to 3
  times higher in Bos indicus/Bos taurus crosses
  than in Bos taurus/Bos taurus crosses)
• -highest in F1, and tends to be proportional to
  degree of heterozygosity
• -especially important for female productivity
  (reproduction and maternal ability)

10
Crossbred Cows

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

11
Maternally Influence Characters

• Performance for a maternally influenced
  character (such as weaning weight) is a function
  of
• 1. breed composition of the calf
• 2. heterosis in the calf (direct)
• 3. breed composition of the dam
• 4. heterosis in the dam (maternal)

12
How to Estimate Heterosis

• There are two major considerations here
• The actual amount of increased performance in
  units of the trait in F1 animals.
• The expected fraction (or percentage) of the F1
  advantage in other types of crosses.

13
How to Estimate Heterosis
F1 animals will exhibit 100 heterosis between
the two breeds involved, but this is 100 of some
actual advantage in performance. For example In
some F1 crosses, this may be 100 of a 25 lb
advantage, and in other F1 crosses this may be
100 of a 40 lb advantage.
14
How to Estimate Percent Heterosis
Heterosis percent (fraction) is based on the
fraction of gene loci in animals that are
expected to have two alleles from two different
breeds. Angus bulls x Hereford cows gt F1
calves These calves are ½ Angus, ½ Hereford, but
100 of their gene loci are heterozygous.
15
How to Estimate Percent Heterosis
If we take F1 bulls and F1 heifers and mate
them F1 bulls (½ A ½ H) x F1 heifers (½ A ½ H)
gt F2 calves (½ A ½ H) The F2 calves are
expected to have ½ heterosis themselves (50
direct), but also benefit from heterosis in cows
(100 maternal).
16
How to Estimate Percent Heterosis
If you know the fractions of the breeds in the
parents, you can estimate the fraction of
heterosis in progeny (based on chance of
inheritance). ½ A ½ H bulls x ½ A ½ Gelbvieh
cows gt ½ A ¼ H ¼ G calves Heterosis in
calves can come from A-G, H-G, H-A combinations,
each has ¼ chance of occurrence. We would say
these calves have 75 heterosis.
17
Heterosis

• Heterosis increases production per cow 20 to 25
  in Bos taurus x Bos taurus crosses and at least
  50 in Bos indicus x Bos taurus crosses in
  subtropical regions.
• More than half of this effect is dependent on use
  of crossbred cows.

18
Cumulative Effects Of Heterosis For Weight Of
Calf Weaned Per Cow Exposed To Breeding
23.3
14.8
Percent
8.5
8.5
Straightbred cows straightbred calves
Straightbred cows X-bred calves
X-bred cows X-bred calves
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Heterosis Utilization is Critical for Commercial
Producers

• Consider pounds of calf weaned per cow exposed
  to breeding
• Cow-calf System Productivity lb
  calf
• Straightbred cows producing
• straightbred calves 100 450
• 2. Straightbred cows producing
• crossbred calves 108.5 488
• Crossbred cows producing
• crossbred calves 123.3 555

Based on data from USDA MARC involving Bos
taurus crosses and purebreds.
20
Heterosis Depends on Crossbreeding System and
Breeds
Type of system Example Direct Maternal Termina
l F1 cross Charolais x Hereford 100
0 Terminal F1 cross Brahman x Hereford 200
0 Two breed rotation Angus, Hereford 67
67 Two breed rotation Angus, Brahman 133 133 Thr
ee breed terminal Charolais x F1
Angus-Hereford 100 100 Three breed terminal
Charolais x F1 Brahman-Hereford 150 200 Three
breed rotation Angus, Simmental, Gelbvieh 86
86 Three breed rotation Angus, Brahman,
Charolais 143 143 Two breed composite 50
Hereford, 50 Simmental 50 50 50 Angus,
50 Brahman 100 100 5/8 Charolais, 3/8 Red
Angus 47 47 5/8 Shorthorn, 3/8 Brahman
84 84 Four Breed Composite 25 each A, H, S,
C 75 75 25 A, Br, C, G 112.5 112.5 2
5 A, Br, L, Nellore 125 125 Some crosses in
the system will exhibit more heterosis than
others.
21
Average birth weights at the McGregor Station
1992-1997 ________________________________________
_______________   Birth Weight (lb) Sire
breed Dam breed bulls heifers
average __________________________________________
_____________   Hereford Hereford 80
76 78   Brahman Brahman 74 71
72.5   Hereford Brahman 75 73
74   Brahman Hereford 101 87
94 _______________________________________________
_______
22
Crossbreeding Systems

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

23
In order for a crossbreeding system to be
sustainable in a region, it should have the
following characteristics
1. It should be possible for all the breeding
stock that are needed for the system to be
produced in the same region where the system will
be operated. 2. The system should be fairly
simple to operate. 3. All cattle used in and
produced by the system should be adapted to the
local environment. 4. There should be no major
incompatibilities between the cattle that are
mated. 5. All animals that are produced in the
system must be acceptable to local market
conditions.
24
Example of Three Breed Composite

• Composite that is ½ Angus, ¼ Charolais, and ¼
  Hereford
• 1/2A 1/4C 1/4H bulls x 1/2A 1/4C 1/4H cows
• gt 1/2A 1/4C 1/4H calves
• Breed combinations in calves can be
• A-C, A-H, or C-H.

25
Breed Combinations in Calves
Cows ½ A ¼ C 1/4H
Bulls ½ A ¼ C ¼ H
¼ A-A 1/8 A-C 1/8 A-H
1/8 C-A 1/16 C-C 1/16 C-H
1/8 H-A 1/16 H-C 1/16 H-H
Heterosis in calves 1/8 1/8 1/8 1/8
1/16 1/16 5/8 or 62.5
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Results From Research Projects
27
LONGEVITY AND LIFETIME PRODUCTION OFSTRAIGHTBRED
HEREFORD (H), ANGUS (A), HEREFORD X ANGUS (HA)
AND ANGUS X HEREFORD (AH) COWS
Breed group Trait
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 lt .05
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TAMU Diallele Project

• Purebred and F1 cows of Angus, Hereford, Brahman,
  Holstein and Jersey were evaluated over a 14 year
  period.
• Only production reason for culling was if cow
  failed to give birth to live calf every 24
  months, or if cow appeared unable to raise
  another calf.

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Breed type Percent remaining Productive life (yr)
Angus 7 10.3
Brahman 17 9.7
Hereford 5 9.8
Holstein 0 7.3
Jersey 0 6.2
Angus-Brahman 38 14.7
Angus-Hereford 22 11.7
Angus-Holstein 14 12.3
Angus-Jersey 8 9.9
Brahman-Hereford 38 13.2
Brahman-Holstein 41 13.6
Brahman-Jersey 22 11.8
Hereford-Holstein 18 11.8
Hereford-Jersey 20 12.0
Holstein-Jersey 0 8.8
30
Research Project in Nebraska
Angus, Hereford and Shorthorn evaluated as
purebred and as F1 crossbred cows for cow
productivity and longevity. Cows born 1960-1963
and were kept until they were 12 to 15 years old.
31
Survival percentage to 12 yr and longevity (kept
to 12-15 yr old)
Breed type Survival () Longevity (yr)
Hereford 19.8 8.5
Angus 43.5 9.4
Shorthorn 13.0 7.3
Hereford-Angus 46.3 10.8
Hereford-Shorthorn 34.9 8.8
Angus-Shorthorn 45.3 9.6
32
Mouth scores based on teeth length in aged cows
Breed type Mouth score
Hereford 11.0
Angus 11.8
Shorthorn 10.3
Hereford-Angus 15.1
Hereford-Shorthorn 16.5
Angus-Shorthorn 13.8
Higher number indicates more tooth remaining.
33
Reasons for Nebraska cows culled
34
TAMU Riesel Project

• Production of F1 calves in 1982-1985 by mating
  Angus, Gray Brahman, Gir, Indu-Brazil, Nellore
  and Red Brahman sires to Hereford cows.
• All cows were kept to measure productivity and
  longevity.
• Udder, teat and teeth soundness evaluated

35
Comparison of F1 Cows at McGregor, TX through 14
years of age
CC lb calf per
still Type of cow BWT WWT weaned
cow exposed in herd Angus-H 86.6
499 83.3 416 53 Gray
Brahman-H 81.6 566 88.4 500
53 Gir-H 76.6 562 91.5 514
73 Indu-Brazil-H 81.8 563
81.0 456 33 Nellore-H 81.1 566
96.1 544 80 Red Brahman-H 81.9
574 86.0 494 43
36
Comparison of F1 Cows at McGregor, TX through 14
years of age
Teats that were too large, and/or udders that
were too pendulous caused increases in calf
illness because it was difficult for calves to
nurse on their own initially. Size of udder did
not appear related to milk production within a
breed. Nellore crossbred cows had smallest teats
and tighest udders, and best overall production
and longevity. All of Bos indicus-Hereford F1
cows had better mouths later in life than
Angus-Hereford F1 cows.
37
Heterosis Retention Project at McGregor, Texas

• Initiated in mid 1990s to measure heterosis
  retention in Bos indicus-Bos taurus crosses.
• Purebred Angus, Hereford, Brahman and Nellore.
• Cow reproduction and productivity major focus of
  project.

38
Heterosis Retention Project - McGregor, TX
Heterosis estimates for individual traits. Heterosis estimates for individual traits. Heterosis estimates for individual traits. Heterosis estimates for individual traits. Heterosis estimates for individual traits.
CCB CCW WWT lb calf/cow
B/A F1 9.5 11 29 lb (6.3) 74 lb (23)
B/H F1 15 15.5 88 lb (20.7) 146 lb (53)

B/A F2 -6.5 -6.0 1 lb (0.2) -30 lb (-9)
B/H F2 13 14.5 42 lb (9.9) 103 lb (37)
39
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.

40
Matching Genetic Potential to the Climatic
Environment (Olson et al., 1991)
41

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

42
Summary

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

43
Bad Breeding Decisions are Costly