Transcript GPVEC Module V - University of Nebraska–Lincoln

Applied Beef Cattle Breeding and Selection
Composite Populations
Larry V. Cundiff
ARS-USDA-U.S. Meat Animal Research Center
2008 Beef Cattle Production Management Series-Module V
Great Plains Veterinary Education Center
University of Nebraska, Clay Center
September 18, 2008
Estimating Heterosis for a specific two breed cross
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 =
HH = 395 =
gA +
gH +
+ mA
+ mH
(.5)(HA + AH) - .5 (AA + HH) = 423 – 400 = 23 = hIah
HA = 430 = .5gH + .5 gA + hIha + mA
AH = 416 = .5gH + .5 gA + hIha + mH
AA = 405 =
HH = 395 =
gA +
gH +
+ mA
+ mH
In the above equations,
HA denotes a crossbred calf with a Hereford sire and an Angus dam.
AH denotes a crossbred calf with an Angus sire and a Hereford dam.
HH denotes a straightbred calf with a Hereford sire and Hereford dam.
AA denotes a straightbred calf with an Angus sire and Angus dam.
gH denotes the additive breed effect for Herefords and gA the additive
breed effect for Angus.
hIha denotes effect of individual hetersosis expressed by Hereford X
Angus or Angus X Hereford reciprocal crosses. Note that hIha = hIha.
mA denotes the maternal (MILK) breed effect for Angus and mH the
maternal breed effect for Hereford dams.
Estimating Maternal Heterosis
C X A = .5gC + .5 gA + hIca + mA
C X B = .5gC + .5 gB + hICB + mB
C X AB = .5gC + .25 gA + .25gB + .5hIAC + .5hIBC + .5mA +
.5 mB + hMAB
C X BA = .5gC + .25 gB + .25gA + .5hIAC + .5hIBC + .5mA +
.5 mB + hMAB
.5[( C X AB) + (C X BA)] – .5[(C X A) + (C X B)] = hMAB
C X A = .5gC + .5 gA + hIca + mA
C X B = .5gC + .5 gB + hICB + mB
C X AB = .5gC + .25 gA + .25gB + .5hIAC + .5hIBC + .5mA +
.5 mB + hMAB
C X BA = .5gC + .25 gB + .25gA + .5hIAC + .5hIBC + .5mA +
.5 mB + hMAB
In the above equations,
the gA, gB and gC denote additive breed effects for breeds A, B and C respectively.
hICA, hICB and hIAC denote individual heterosis effects for C X A (or A X C) , C X
B (or B X C) , and A X C (or C X A) breed crosses, respectively.
mA and mB denote maternal (MILK) breed effects for breeds A and B,
respectively.
hMAB denotes maternal heterosis expressed by A X B (or B XA) crossbred dams.
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
MARC I
¼ Limousin, ¼ Charolais,
¼ Brown Swiss,
c Angus and c Hereford
Angus
MARC II
¼ Simmental, ¼ Gelbvieh,
¼ Hereford and ¼ Angus
MARC III
¼ Pinzgauer, ¼ Red Poll,
¼ Hereford and ¼ Angus
Limousin
Simmental
Pinzgauer
Charolais
Gelbvieh
Red Poll
Brown Swiss
(Braunvieh)
Hereford
Hereford
Angus
Angus
Hereford
HETEROSIS EFFECTS AND RETAINED HETEROSIS
IN COMPOSITE POPULATIONS VERSUS CONTRIBUTING
PUREBREDS (Gregory et al., 1992)
Trait
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
Calf crop born, (mat.), %
Calf crop wnd., (mat.), %
200 d wn. wt./cow exp. (mat.), lb
Composites minus purebreds
F1
F2
F3&4
3.6
42.4
57.3
63.5
-21
.51
33
5.4
6.3
55
5.0
33.4
51.4
58.6
-18
.35
36
1.7
2.1
37
5.1
33.7
52.0
59.8
-17
.43
Composite populations
maintain heterosis
proportional to heterozygosity
(n-1)/n or 1 – S Pi2
MODEL FOR HETEROZYGOSITY IN
A TWO BREED COMPOSITE
Breed
Dam
Breed of sire
½A
½B
½A
½B
¼ AA
¼ BA
(n-1)/n or 1 – S Pi2 = .50
¼ AB
¼ BB
MODEL FOR HETEROZYGOSITY IN
A THREE BREED COMPOSITE
Breed
Dam
.50 A
.25 B
.25 C
Breed of sire
.50 A
.25 B
.25 AA
.125 BA
.125 AC
.125 BA
.0625 BB
.125 BC
1 – S Pi2 = (1 - .375) = .625
.25 C
.125 CA
.0625 CB
.0625 CC
Weaning Wt Marketed Per Cow Exposed for Alternative
Crossbreeding Systems Relative to Straightbreeding (%)
System
Hi
(+ 8.5%)
Hm
(+14.8%)
Wean. wt
marketed
per cow exp
0
Straight breeding
0
0
2-breed rotation (A,B)
3-breed rotation (A,B,C)
4-breed rotation (A,B,C,D)
.67
.86
.93
.67
.86
.93
15.5
20.0
21.7
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)
.47
.5
.625
.75
.47
.5
.625
.75
11.0
11.7
14.6
17.5
F1 bull rotation (3-breed: AB, AC)
F1 bull rotation (4-breed: AB, CD)
.67
.83
.67
.83
15.5
19.3
Composite populations provide for
effective use of
• Heterosis
• Breed differences
• Uniformity and end product
consistency
Genetic Variation in Alternative Mating Systems
Optimum
Assumes that the Two F1’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.
CEFFICIENTS OF VARIATION IN PUREBRED AND
COMPOSITE POPULATIONS (Gregory et al., 1992)
Trait
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
Purebreds
.01
.11
.09
.08
.09
.08
.07
.07
.02
.08
.10
.04
.19
Composites
.01
.12
.09
.08
.09
.07
.07
.08
.02
.08
.10
.06
.20
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
Rotational and Terminal Sire
Crossbreeding Programs
Cow
Age
2 Breed Rotation

No.
A
1
2
3
20
18
15
45%
4
5
12
13
12
1
55%
Lbs. Calf/Cow
B
Two Breed
Composite
1/2A - 1/2B

T x (A-B)
21%
T x (A-B)
18%
Weaning Wt Marketed Per Cow Exposed for Alternative
Crossbreeding Systems Relative to Straightbreeding (%)
System
Hi
+ 8.5%
Hm
+14.8%
Straight breeding
0
0
2-breed rotation (A,B)
3-breed rotation (A,B,C)
4-breed rotation (A,B,C,D)
.67
.86
.93
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)
Wean. wt
Terminal
marketed
crossa
per cow exp (+5% wt/calf)
0
0
.67
.86
.93
15.5
20.0
21.7
20.8
24.1
25.4
.47
.5
.625
.75
.47
.5
.625
.75
11.0
11.7
14.6
17.5
17.3
17.8
20.3
22.2
.67
.83
.67
.83
15.5
19.3
20.8
23.6
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).
SUMMARY
General Considerations
• Rotational Systems
Provide for more effective use of
• Heterosis
• Composite populations
Provide for more effective use of
• Breed differences
• Uniformity and end product consistency
Figure 6. Use of heterosis, additive breed effects and
Complementarity with alternative crossbreeding systems.
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.
Module IV Applied Animal Breeding and Selection
Homework questions assigned September 18
To be returned by October 23, 2008
(Email to: [email protected])
The Brangus breed has a genetic composition of 5/8 Angus and 3/8 Brahman breeding.
1) What is the expected heterozygosity or level of Brahman X Angus heterosis expected in the Brangus
breed (show work)?
2) How would you expect the effect of heterosis for Brangus to compare to that in a breed with a
composition of 5/8 Angus and 3/8 Shorthorn, why or why not? (In other words, would effects of
heterosis be the same, or more, or less for Brahman X Angus crosses than for Angus X Shorthorn
crosses, why or why not?)
3) What is the expected level of heterosis in a four breed composite founded with ¼ breed A, ¼ breed
B, ¼ breed C, and ¼ breed D inheritance (show work)?
4) State the location and describe a typical production environment for cow herds where you reside or
provide service.
5) If you were to develop a composite population adapted to this production environment, what
foundation breeds would you select?
6) What proportions of each breed would you use in the composite population?
7) What would the expected level of heterosis be in your composite population (show work)?
8) Why would you select these breeds (Discuss the merits of each breed selected for additive direct and
maternal breed effects).