1. Applied Beef Cattle Breeding and Selection
Inbreeding and Heterosis in Beef Cattle
Larry V. Cundiff
ARS-USDA-U.S. Meat Animal Research Center
2008 Beef Cattle Production Management Series-Module IV
Great Plains Veterinary Education Center
University of Nebraska, Clay Center
August 1, 2008

2. Homework Participants Module 2 Module 3 Anderson Castleberry DavidsonX
Fox
Frese
Furman
Jones
Langon
Linhart
Matlick
Van Boening
Werhman
Ondrack

3. homework to

4. Degrees of inbreeding according to relationship of mates (Lush, 1945)
Species
crosses
Outbreeding
within a
breed
First
cousin
Full
sib
Self
Fertili-
zation
Half
sib
Random
Mating
In a pure
breed
Cross
breeding

5. Zygotic Frequency with Self Fertilzation of a Heterozygote (Aa)
Female
gamete
Male gamete
.5 A
.5 a
.25 AA
.25 Aa
.25 aa

6. Change in genotypic frequency with
self fertilization
Generation AA Aa aa
100 1 25 50 2
37.5 3
43.75
12.5 4
46.875
6.25 5
3.125 …
Various
but many

7. Effects of different degrees of dominance on phenotypic value
(additive)
Partial
dominance
Complete
dominance

8. Effects of inbreeding on heterozygosity/homozygosity
Zygous
line
Inbred
Line
F = .5
Sire
Daughter Or
Full sib
Pure
Breed
Random
mated
Cross
breeding ?
100 80 60 40 20 H O M Z Y G S I T
(%) AA aa E R Aa
Effects of inbreeding on heterozygosity/homozygosity
(Cundiff and Gregory, 1977) ?

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

10. Effects of inbreeding in cattle
(Brinks et al., 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.

11. Estimating Heterosis for a specific two breed cross
Sire breed
Dam breed
Calf breed
Weaning wt H A HA
430 AH
416 AA
405 HH
395
HA = 430 = .5gH gA + hIha + mA
AH = 416 = .5gH gA + hIha + mH
AA = 405 = gA mA
HH = 395 = gH mH
(.5)(HA + AH) + .5 (AA + HH) = 423 – 400 = 23 = hIah

12. Estimating Maternal Heterosis
C X A = .5gC gA + hIca + mA
C X B = .5gC gB + hICB + mB
C X AB = .5gC gA + .25gB + .5hIAC + .5hIBC + .5mA +
.5 mB + hMAB
C X BA = .5gC gB + .25gA + .5hIAC + .5hIBC + .5mA +
.5[( C X AB) + (C X BA)] – .5[(C X A) + (C X B)] = hMAB

13. Crossbred calves (individual heterosis)
HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUS BREEDS FROM DIALLEL CROSSING EXPERIMENTS
Bos taurus X Bos indicus X
No Bos taurus No Bos taurus
Trait Est Units % Est. Units %
Crossbred calves (individual heterosis)
Calving rate, %
Survival to weaning, %
Birth weight, kg
Weaning weight, kg
Postweaning ADG, g/d
Yearling weight, kg
Cutability, %
Quality grade, 1/3 gr

14. Bos taurus X Bos indicus X
HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUS BREEDS FROM DIALLEL CROSSING EXPERIMENTS
Bos taurus X Bos indicus X
No Bos taurus No Bos taurus
Trait Est Units % Est. Units %
Crossbred cows (maternal heterosis)
Calving rate, %
Survival to weaning
Birth weight, kg
Weaning weight, kg
Longevity, yrs
Lifetime prod.
No. Calves
Cum. wn. wt., kg

15. Weight of Calf Weaned Per Cow
Heterosis
Weight of Calf Weaned Per Cow
Exposed To Breeding
23.3
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.
14.8
Percent
8.5
8.5
This slide summarizes results from a longterm heterosis project completed in the 1970’s comparing production of straightbreds and crosses in all combinations among the Hereford, Angus, and Shorthorn breeds.
Weaning wt per cow exposed was increased 8.5 % by raising cross bred calves.
However the greatest advantages of crossbreeding depended on use of crossbred cows.
Weaning wt per cow exposed was increased 23 % in crossbred cows raising three way cross progeny. More than half of total heterosis effect was dependent on use of crossbred cow to take advantage of their improved reproduction rate and milk production.
In addition, longevity was increased, herd life was 1.9 yr longer for F1 cows than for straightbred cows. Break even cost so production were reduced 10%, these are savings that as essential today as ever, if the beef industry is to remain competitive with other meat products.
X-bred
cows
calves
Straightbred
cows
straightbred
calves
Straightbred
cows
X-bred
calves

16. ANGUS (HA) AND ANGUS X HEREFORD (AH) COWS
LONGEVITY AND LIFETIME PRODUCTION OF STRAIGHTBRED HEREFORD (H), ANGUS (A), HEREFORD X
ANGUS (HA) AND ANGUS X HEREFORD (AH) COWS
Breed group
Trait H A HA AH Heterosis
Longevity, yrs *
Lifetime production
No. calves *
Wt of calves weaned, lb *
HA and AH were superior to either parent breed bred straight
1.9 extra years (21%)
1.3 extra calves (20%)
766 extra pounds = 1.8 extra calves with straightbred dams.
Heterosis in Bos indicus X Bos taurus crosses about 2 X this magnitude
*P < .05

18. Conclusions Heterosis Effects are greatest for lowly heritable traits:
Reproduction
Survival
Longevity
Heterosis effects are moderate for moderately
heritable traits:
Direct and maternal weaning weight
Postweaning gain
Heterosis effects are small for highly heritable traits:
Feed efficiency
Carcass traits
Retail product %
Fat thickness
Marbling

19. Static Three-breed Cross System
Offspring marketed
Pounds of calf/cow
increased about19%
45-50%
of Cows
25-30%
25%   A B C A AB

20. Rotational Crossbreeding Systems
Sig heterosis maintained in rotational systems (H, A, S)
68% of max heterosis, or 15% increase in lbs calf weaned
86% or 19% increase in wn wt per cow exp in 3 breed rotational system

21. Heterosis for Production Per Cow in Hereford,
Angus, and Shorthorn Rotational Crosses
First Generation
Observed (%)
Expected (%)a
Second Generation
Observed (%)
Expected (%)a
aBased on individual and maternal heterosis observed in F1 generation and assumes that retained heterosis is proportional to retained heterozygosity.
Two breed Three breed
rotation rotation

22. Genetic Composition and Heterosis Expected in a Two-Breed Rotation
Heteroz. of Est.
Additive genetic progeny in wt.
comp. of progeny relative to F wnd/cowa
Sire A B
Generation breed % % % %
1 A
2 B
3 A
4 B
5 A
6 B
7 A
aBased on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits, when loss of heterosis in proportional to loss of heterozygosity

23. Genetic Composition and Heterosis Expected in a
Three-Breed Rotation
Additive Genetic Heteroz. of Est. increase
Comp. of Progeny progeny in wt.
Sire A B C relative to F1 wnd/cowa
Generation breed % % % % %
1 A
2 B
3 C
4 A
5 B
6 C
7 A
8 B
aBased 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.

24. Rotational Crossbreeding Systems
Sig heterosis maintained in rotational systems (H, A, S)
68% of max heterosis, or 15% increase in lbs calf weaned
86% or 19% increase in wn wt per cow exp in 3 breed rotational system

25. Rotational crossing systems maintain heterosis proportional to heterozygosity

26. Next time : Composite Populations
and alternative crossbreeding systems.

28. Brown Swiss (Braunvieh)
MARC I
¼ 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
3 composite pops.
75:25, 50:50, 25:75 Continental to British

29. Composites minus purebreds
HETEROSIS EFFECTS AND RETAINED HETEROSIS IN COMPOSITE POPULATIONS VERSUS CONTRIBUTING PUREBREDS (Gregory et al., 1992)
Composites minus purebreds
Trait F F2 F3&4
Birth wt., lb
200 d wn. wt., lb
365 d wt., females, lb
365 d wt., males, lb
Age at puberty, females, d
Scrotal circumference, in
200 d weaning wt., (mat.), lb 33 36
Calf crop born, (mat.), %
Calf crop wnd., (mat.), %
200 d wn. wt./cow exp. (mat.), lb 55 37
Sig heterosis maintained in composite pops into F3 and and F4 generations
~ 75 % of F1 heterosis on average over all composites and for most traits
Proportional to increased heterozygosity expected

30. Composite populations maintain heterosis proportional to heterozygosity (n-1)/n or 1 – S Pi2

31. Rotational crossing systems or composite populations maintain significant heterosis

32. MODEL FOR HETEROZYGOSITY IN
A TWO BREED COMPOSITE
Breed Breed of sire
Dam ½ A ½ B
½ A ¼ AA ¼ AB
½ B ¼ BA ¼ BB
(n-1)/n or 1 – S Pi2 = .50

33. MODEL FOR HETEROZYGOSITY IN A THREE BREED COMPOSITE
Breed Breed of sire
Dam A B C
.50 A AA BA CA
.25 B BA BB CB
.25 C AC BC CC
1 – S Pi2 = ( ) = .625

34. Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%)
Wean. wt
H i Hm marketed
System (+ 8.5%) (+14.8%) per cow exp
Straight breeding
2-breed rotation (A,B)
3-breed rotation (A,B,C)
4-breed rotation (A,B,C,D)
2-breed composite (5/8 A, 3/8 B)
2-breed composite (.5 A, .5 B)
3-breed composite (.5A, .25 B, .25C)
4 breed composite (.25A,.25B,.25C,.25D)
F1 bull rotation (3-breed: AB, AC)
F1 bull rotation (4-breed: AB, CD)

35. Composite populations provide for effective use of
Heterosis
Breed differences
Uniformity and end product consistency

36. Genetic Variation in Alternative Mating Systems
Optimum
Assumes that the Two F1’s Used are of Similar Genetic Merit

37. 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.
Consistent with results in earlier cycles of the program, genetic potential for quality grade and yield grade are still more nearly optimized in cattle with 50:50 ratios of Continental to British inheritance than in cattle with higher or lower ratios of Cont. to British inheritance.

38. COMPLEMENTARITY is maximized in terminal crossing systems Cow Herd
Small to moderate size
Adapted to climate
Optimal milk production
for feed resources
Terminal Sire Breed
Rapid and efficient growth
Optimizes carcass composition
and meat quality in
slaughter progeny
Progeny
Maximize high quality lean beef
produced per unit feed consumed
by progeny and cow herd

39. Rotational and Terminal Sire Crossbreeding Programs
Cow
Age No.
1 20
2 18
3 15
2 Breed Rotation
Two Breed Composite  A B
1/2A - 1/2B 
45%
4 13
5 12
- -
12 1
T x (A-B)
T x (A-B)
55%
Lbs. Calf/Cow
21%
18%

40. Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%)
Wean. wt Terminal
H i Hm marketed crossa
System % % per cow exp (+5% wt/calf)
Straight breeding
2-breed rotation (A,B)
3-breed rotation (A,B,C)
4-breed rotation (A,B,C,D)
2-breed composite (5/8 A, 3/8 B)
2-breed composite or F1 bulls (.5 A, .5 B)
3-breed composite (.5A, .25 B, .25C)
4 breed composite (.25A,.25B,.25C,.25D)
F1 bull rotation (3-breed: AB, AC)
F1 bull rotation (4-breed: AB, CD)
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).

41. SUMMARY

42. Figure 6. Use of heterosis, additive breed effects and
Complementarity with alternative crossbreeding systems.

44. Implications for Crossbreeding
Similarity in mean performance of British and Continental European breeds means they are more suited for use in rotational cross-breeding systems today than 30 years ago
Performance levels are not expected to fluctuate as much with rotational crossing for growth traits and cow size . Growth rate can be stabilized by using Across-breed EPDs.
Differences in birth weight are still significant and warrant use of sire breeds with lighter birth weight on first calf heifers (i.e., Angus, Red Angus, etc.).
Intergeneration fluctuations in milk production still persist but they are less than half as great as 30 years ago. Milk levels can be stabilized by using Across-breed EPDs.

45. Implications for Crossbreeding
Advantages of terminal sire crossing systems are not as great today as 30 years ago due to similarity of breeds for rate and efficiency of growth.
However, differences between British and Continental breeds in carcass traits are still significant and relatively large.
Inter generation fluctuations in mean performance for carcass traits are still large and significant.
For carcass traits, uniformity and end-product consistency can still be enhanced by use of composite populations or hybrid bulls.
Adaptation to intermediate subtropical/temperate environments can be optimized with greater precision by use of composite populations or hybrid bulls.

47. Heterosis proportional to heterozygosity in various matings
Mating type Progeny Dam
Pure breed 0 0
Two breed F1 cross (A x B) 100 0
F2 (AB x AB)
F3 (AB x AB) (or F4, ..Fn) = 2 breed Composite 50 50
Backcross (A x AB)
1st backcross interse (A-AB x A-AB)
¾-1/4 composite (.75A, .25B)
5/8-3/8 composite (.625 A, .375 B) 47 47
2 breed rotation 67 67
Three way cross (A x BC)
1st 3-way interse (A - BC) x (A-BC)
3 –breed composite (.5 A, .25 B, .25C)
3 breed rotation (A, B, C) 86 86
Rotation F1 hybrids, 1 common breed (AB -AC) 67 67
Four way cross
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

48. Rotational and Terminal Sire Crossbreeding Programs
Cow
Age No.
1 20
2 18
3 15
2 Breed Rotation
3 Breed Rotation  B A B   
45% A  C
4 13
5 12
- -
12 1
T x (A-B)
T x (A-B-C)
55%
Lbs. Calf/Cow
21%
24%

49. an important genetic resource
BREED DIFFERENCES
an important genetic resource
Cross breeding of composite populations can be used to exploit:
HETEROSIS
COMPLEMENTARITY among breeds optimize performance levels for important traits and to match genetic potential with:
Market preferences
Feed resources
Climatic environment

50. Composite populations provide for effective use of
Heterosis
Breed differences
Uniformity and end product consistency

51. Trait Purebreds Composites
CEFFICIENTS OF VARIATION IN PUREBRED AND COMPOSITE POPULATIONS (Gregory et al., 1992)
Trait Purebreds Composites
Gestation length, d
Birth wt
200 d wn. wt
365 d wt., females
365 d wt., males
Age at puberty (females)
Scrotal circumference
5 yr cow wt, lb
5 yr height, in
Steer carcass wt, lb
Rib-eye area
Retail product, %
Retail product, lb
Sig heterosis maintained in composite pops into F3 and and F4 generations
~ 75 % of F1 heterosis on average over all composites and for most traits
Proportional to increased heterozygosity expected

52. COMPLEMENTARITY is maximized in terminal crossing systems Cow Herd
Small to moderate size
Adapted to climate
Optimal milk production
for feed resources
Terminal Sire Breed
Rapid and efficient growth
Optimizes carcass composition
and meat quality in
slaughter progeny
Progeny
Maximize high quality lean beef
produced per unit feed consumed
by progeny and cow herd

53. General Considerations
Rotational Systems
Provide for more effective use of
Heterosis
Composite populations
Breed differences
Uniformity and end product consistency

55. Composite populations provide for effective use of
Heterosis
Breed differences
Uniformity and end product consistency

56. Effect of Heterosis on Percentage Cows Remaining in Herd
At Different Ages Relative to Those Originally Retained
as Breeding Heifers
Crossbred cows
Straightbred cows
Percentage Cows Remaining
Age At Exposure to Breeding (years)

57. Rotational Crossbreeding Programs  A B A B    C
Increase Lbs. Calf
Per Cow 15%
Increase Lbs. Calf
Per Cow 19%

58. Genetic Variation in Alternative Mating Systems
Optimum
Assumes that the Two F1’s Used are of Similar Genetic Merit

59. Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%)
Wean. wt Terminal
H i Hm marketed crossa
System % % per cow exp (+5% wt/calf)
Straight breeding
2-breed rotation (A,B)
3-breed rotation (A,B,C)
4-breed rotation (A,B,C,D)
2-breed composite (5/8 A, 3/8 B)
2-breed composite or F1 bulls (.5 A, .5 B)
3-breed composite (.5A, .25 B, .25C)
4 breed composite (.25A,.25B,.25C,.25D)
F1 bull rotation (3-breed: AB, AC)
F1 bull rotation (4-breed: AB, CD)
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).