Transcript Beef Cattle Genetics - West Virginia University

West Virginia University
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Genetics in Beef Cattle
Wayne R. Wagner
West Virginia University
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•
A Beef Animal’s Phenotype is completely
determined by:
1) It’s genetic makeup



Cattle have 30 pairs of chromosomes
Genes located on chromosomes transmitted from parent to
offspring
Genes code for production of proteins/enzymes
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• Quantitative – traits influenced by very few gene
pairs. There is a distinct difference in phenotypes.
Example horned vs polled or red vs black.
Let B = Black
b = Red
Heterozygous X Heterozygous
B
b
BB
B
black
b
Bb
black
Bb
black
Bb
red
25% Homozygous Black
50% Black w/Red Gene
25% Red
Heterozygous X Red
b
b
B
Bb
black
Bb
black
b
bb
red
bb
red
50% Black w/Red gene
50% Red
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• Qualitative – traits influenced by many pairs of
genes. Show continuous variations or gradual
variation from one extreme to the other.
Expression of these traits is influenced by the
environment.
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•
A Beef Animal’s Phenotype is completely
determined by:
2) The Environment in which the animal is raised
A. Unknown




Includes weather (temperature, humidity, precipitation)
Disease, internal & external parasites (vaccination program)
Feed/forage both quality and amount
Unique factors including injury/sickness
B. Known



Age of dam
Age of calf
Sex of calf
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The differences between two Hereford
calves born in 2006 are due to
differences in genetics and the
environments in which they are raised.
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• Beef producers keep records on various traits
(Calving Ease, Weaning Weight, Yearling Weight,
Scrotal circumference, IMF, REA)
– These records are adjusted for known sources of
variation so differences are due to genetics and unknown
Environment → improves accuracy
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Additive
G
Non-additive
P
Known
E
Unknown
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• The objective of a seedstock producer is to limit
differences due to Environmental effects as much
as possible to get the best estimate of true genetic
differences!
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• Contemporaries – calves born in a
similar time frame and then raised
together and treated alike.
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• Contemporary information is
important because it is used in the
computation of EPD’s.
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• EPD’s – Expected Progeny Difference
– Allows you to compare two bulls of the same breed but
raised in different environments and under different
health and nutritional programs.
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• EPD’s reported in actual units.
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• EPD’s are for within breed
comparisons.
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• EPD’s are not static – change as
new and more data is collected.
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• EPD is our best estimate of an animal’s genetic value for a
particular trait at a specific time and given the information
that is available at that time.
– ie. In March 2006 you buy a yearling bull with a YW EPD of 70
lbs.
• In 2006 his dam raises another calf & yearling data is collected in
March 2007
• In 2006 his sire produces 3000 additional progeny with yearling
data collected in 2007
• The data added in 2007 updates the estimate of genetic value for
the dam to a small degree and to the estimate of genetic value of
the sire to a somewhat larger degree.
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• EPD’s depend upon accurate
contemporary information being
reported.
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• EPD’s are estimates of how future
progeny will perform when mated at
random to the average of the
breed.
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• Breed average EPD’s ≠ 0
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• Acc is a measure of risk associated with
an EPD. Acc is an indication of how much
an EPD might change as additional data is
collected.
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• Acc ranges from 0 – 1
– Acc below .4 would be low
– Acc between .4 and .8 are moderate
– Acc above .8 are high
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• Acc is an indication of how much an EPD
might change. (Possible Change)
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Acc
.2
.4
.6
.8
.95
Possible Change Values for Different Traits Angus
CED
YW
Milk
IMF
REA
6.2
4.7
3.2
1.6
.4
13.6
10.2
6.8
3.4
.9
7.8
5.8
3.9
1.9
.5
.14
.11
.07
.04
.01
.26
.20
.13
.07
.02
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• If you produce your own replacement females, the
last 3 bulls used in a calf’s pedigree accounts for
87 ½ of the genetic makeup and potential.
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• The value of a herd depends upon the bulls used.
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• Often times, when cattle are raised in an excellent
environment, it is difficult to determine how much of
an animals superiority is due to nutrition,
vaccination programs, etc and how much is
genetic.
Breed Average EPD’s (Non-Parent)
Breed
Trait
Angus
Charolais
Hereford
Gelbvieh
Limousin
Maine Anjou
Red Angus
Simmental
BW YW
Milk
2.3
1.3
3.8
1.8
1.9
.7
.3
2.0
20
5.9
15
18
19.4
15.6
16
5.3
74
36
65
74
70
71
53
59
GL
-1.4
Scrotal IMF REA
Circum
.12
.21
.5
.6 .00
.4 -.03
.3 .00
.13
.08
.12
.07
.07
.05
.04
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• Crossbreeding
– Heterosis – advantage of crossbred animal compared to
average of parental breeds.
– Complementarity – combination of breed strengths.
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• Heterosis:
– Traits with low levels of heritability usually show
significant amounts of heterosis.
– Improves an animal’s ability to withstand stress.
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Economically Important Traits
1) Reproduction/Fertility
a)
b)
c)
d)
Calving Ease
Gestation Length
Scrotal Circumference
Cycling before breeding season starts
2) Feed Efficiency
a) Difficult to measure
b) Indicators – ADG & YW (should be within a frame size)
3) Product Merit
a) REA
b) Marbling
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• Future
–
–
–
–
Feed Efficiency – RFI
Fleshing Ability
Marker Assisted Selection
Balance/Optimums
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• Why RFI?
– Feed:gain determines variable costs and is influenced by
environment, body condition, appetite, stage of growth
and rate and composition of gain.
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• Genetic makeup is the foundation of a cow herd.
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www.nbcec.org
www.beefimprovement.org
www.angus.org
www.hereford.org
www.simmental.org
www.charolaisusa.com