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CRICOS 00026A
AVBS1002 Pig Genetics and Breeding
Presented by
A/Prof Chris Grupen
Telephone: 9036 7740
Email: christopher.grupen@sydney.edu.au
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Key concepts
Learning Objective
– Develop an understanding of the genetics and breeding issues most
important to the pig industry
Learning Outcomes
1. Demonstrate a basic understanding of the heritability of different traits and
how they can be improved by cross-breeding
2. Have knowledge of the common pig breeds in Australian commercial herds
and explain why they are used
3. Describe the strategies used to improve herd genetics
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Simple genetic inheritance
– Controlled by a single gene
– Simple recessive (both copies of the gene)
– Simple dominant (only one copy of the gene)
– Sex-linked recessive (gene on the X-chromosome)
– Not many economically important traits are of this type
Multigenic (polygenic) inheritance
– Determined by a group of genes
– Most of the economically important traits are of this type
Genetic inheritance
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– Performance of an animal is influenced by the parents’ (sire and dam) genetics and the
environment
– Phenotype = Genotype + Environment
– Environment includes but is not limited to nutrition, housing, health status, and thermal conditions
– Some traits are more heavily influenced by environment than by genotype
– Heritability is the proportion of the variance of a trait within a population that is due to genetic
factors
– Heritability is expressed as: H2 = Vg/(Vg + Ve)
– Vg is the variance due to genetics
– Ve is the variance due to environment
Basics of pig genetics and heritability
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– The heritability estimates range from 0 to 1
– Growth and carcass traits have high heritability (>0.30)
– Reproductive traits have low heritability (<0.25)
Heritability of different traits
Growth and carcass traits
Live weight gain 0.30-0.60
Lean tissue growth 0.40-0.60
Feed intake 0.30-0.60
Backfat 0.40-0.70
Carcass length 0.40-0.60
Loin muscle area 0.40-0.60
Ham shape 0.40-0.60
Meat quality 0.30-0.50
Reproductive traits
Ovulation rate 0.10-0.25
Embryo survival 0.10-0.25
Litter size 0.10-0.20
Piglet survival 0.05-0.10
Readiness to rebreed 0.05-0.10
Milk yield 0.15-0.25
Sow longevity 0.10-0.20
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Reasons for selecting a specific trait
– Economically important
– Relatively easy to improve
– Readily measured
– Moderate to high heritability
– Plenty of variation in the population
Why are reproductive traits such as litter size only occasionally selected for?
Traits usually selected for
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Heterosis refers to the improvement in the trait of hybrid animals relative to the parent
populations
– Maternal heterosis
– In female hybrids, compare female only traits (her own vs the average of her dam’s and sire’s
populations)
– Applies mainly to traits relevant from conception to weaning (eg. litter size)
– Offspring heterosis
– In hybrids of both sexes, compare traits that apply to all pigs (their own vs the average of their dam’s and
sire’s populations)
– Applies to traits important to the individual pig throughout its life (eg. growth and carcass properties)
– Paternal heterosis
– In male hybrids, compare male only traits (his own vs the average of his dam’s and sire’s populations)
– Applies mainly to traits relevant at mating (eg. size of testes and sperm concentration)
Heterosis (hybrid vigour)
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Heterosis (hybrid vigour) improves litter size
– Average in parents (12.9 + 13.2)/2 = 13.05 piglets
– Improvement in hybrid (14.3 – 13.05) = 1.25 piglets
– Heterosis value (1.25/13.05)*100 = 9.6%
As the heritability of a trait increases, the heterosis value decreases
Example of cross breeding
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12
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LW Landrace Hybrid
Li
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iz
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(b
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iv
e)
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Cross breeding has achieved:
– More piglets born alive
– Increased piglet birth weight
– Less variation in piglet birth weight
– Improved milk production
– More piglets reared
– Improved fertility
– Improved libido in the boar
– Improved conformation of teats and legs in sows
– Increased sow longevity
Benefits of cross breeding
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Female pigs need to be good at:
– Reproduction
– Good farrowing frequency
– Growth
– Feed conversion efficiency (FCE)
– Lean meat production
– Closely associated with FCE
Male pigs need to be good at:
– Growth
– Lean meat production
Commercial pork production
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Common pig breeds in Australia
Landrace Large White
Duroc Hampshire
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– Fast growing
– Good FCE
– Lean carcass
– Good litter size
– Good farrowing frequency
Large White
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– Fast growing
– Good FCE
– Lean carcass
– Good litter size
– Good farrowing frequency
Landrace
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– Fast growing
– Good FCE
– Lean carcass
– Moderate litter size
– Good farrowing frequency
Duroc
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– Fast growing
– Good FCE
– Lean carcass
– Poor litter size
– Moderate farrowing frequency
Hampshire
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– Poor growth rate
– Poor FCE
– Fat carcass
– Moderate litter size
– Moderate farrowing frequency
Berkshire
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– Poor growth rate
– Poor FCE
– Fat carcass
– Moderate litter size
– Moderate farrowing frequency
Large Black
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– Poor growth rate
– Poor FCE
– Fat carcass
– Moderate litter size
– Moderate farrowing frequency
Tamworth
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– Poor growth rate
– Poor FCE
– Fat carcass
– Good litter size
– Good farrowing frequency
Wessex Saddleback
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Which breeds meet the female requirements?
– High litter size, good farrowing frequency, high growth rate, good FCE and lean
carcass
1. Large White
2. Landrace
Which breeds meet the male requirements?
– High growth rate, good FCE and lean carcass
1. Large White
2. Landrace
3. Duroc
4. Hampshire
Which pig breeds would you choose?
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Females
– Large White x Landrace is the preferred mix
Males
– Breeds available are Large White, Landrace,
Duroc and Hampshire
– Can use the purebred boar
– However, it is more common to use terminal sire lines
(TSLs) which are mixes of 2 or more of these breeds
• Aim is to maximise growth of the offspring
produced
Complementarity
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– Commercially available semen from TSLs
– Extensive performance testing and trait evaluation
– eg. Pig Improvement Company (PIC) products
• Genetic database started in 1983 with data on over 5.6 million animals
Terminal Sire Lines (TSLs)
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Strategies used to improve herd genetics:
1. Boar selection
– On-farm performance and progeny testing
2. Heterosis (hybrid vigour)
– Typically achieved by crossing terminal sire lines with maternal sow lines that differ in breed
composition
3. Bring in new genetics
– Introduce genes for a specifically required characteristic (mainly introduced through purchased
semen)
How is continual genetic improvement achieved?
Managing a breeding program
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– EBVs better predict genetic differences because
they are adjusted for environmental factors and
incorporate knowledge about heritabilities and
genetic correlations
– In Australia, the National Pig Improvement
Program (NPIP) has developed genetic evaluations
for LW, Landrace and Duroc populations
– Software package called PIGBLUP uses best linear
unbiased prediction (BLUP) to calculate EBVs
– Analyses large data sets for breeders
– Monitor genetic progress and management decisions
Estimated Breeding Values (EBVs)
http://agbu.une.edu.au/pig_genetics/pdf/Info%20sheets/producer1.pdf
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