Poultry GeneticsPoultry Genetics AgScience Poultry Science Curriculum Section 2 Historical Overview...
Transcript of Poultry GeneticsPoultry Genetics AgScience Poultry Science Curriculum Section 2 Historical Overview...
Historical Overview
Bird used prior to 1950s were dual purpose
1950s saw introduction of breeding for a specific purpose
Dual Purpose
Meat Production
Egg Production
Dual purpose birds were used
primarily for egg production, and
occasionally used for meat
Watt Publishing, 122 S. Wesley Ave., Mt. Morris, IL 61054 USA
Chickens used for meat production are called
broilers. Broilers are a genetic cross of the
Cornish breed and the White Plymouth Rock
Breed
Chickens used for egg
production are the Leghorn
breed
Historical OverviewDecision to move to breeds specifically for meat and eggs was very important
• These two factors are negatively correlated
• If a hen produces eggs well she will not grow well
Perf
orm
ance
Meat Eggs Meat Eggs
Perf
orm
ance
1960s, 70s, 80s saw more improvement in genetics and increased breeding for and production of white meat
1990s, 2000s development of specialized genetics to meet market demands
• Small bird – Fast food market, Big bird – debone market
Broiler Leghorn
Historical Overview
Companies also began selecting for specialized traits for males and females
Traits emphasized in males:• Meat yield• Weight for age• Days to market• Feed efficiency• Body conformation• Fat content
Traits emphasized in females:• Fertility• Hatchability• Age at sexual onset• Rate of egg production • Growth performance is still monitored
**In recent years males have also been selected for reproductive performance
Historical OverviewGeneticists use heritability for making genetic selection
• Heritability – the ability of measurable traits to be transmitted from parents to offspring
• Traits with high heritability as passed well from parent to offspring
• High heritability = rapid genetic progress between generation
• Low heritability = more generations to improve upon selected trait
Geneticists have focused on improving broiler breast meat yield
• Domestic preference for white meat
• Highly heritable trait
Selection PressureLevel of selection pressure applied and the amount genetic progress are closely related
• Selection pressure – Amount of pressure applied to a selection criteria
• Increased selection pressure = fewer birds selected
• Fewer birds selected = increased genetic progress with each generation
Body weights
Dis
trib
uti
on
Selected Population
Flock A
Body weights
Dis
trib
uti
on
Selected Population
Flock B
Flock B will have increased body weight compared to Flock A because of the greater selection pressure applied
Genetic Improvement: Natural AttributesTwo natural attributes have attributed to the genetic improvement of poultry:
• Hens produce a large number of eggsMore offspring = more opportunity for genetic progress within one generation
• Short generation interval 20-25 weeks a hen will come into production
One hen will produce
dozens of offspring
Lots of options available and
can choose the “best” for breeding
Because of short generation interval risks
have been low and opportunity for
improvement high
Reproduce few offspring over a long period of
time
2 years
Choose the best to reproduce; options
are limited 2 years
Finally, genetic progress but has taken several years; high risk, low
opportunity for improvement within one generation
Genetic Improvement: Important InventionsTwo innovations have been critical to the success of poultry breeding programs:
Trap-nests – Nest used to keep hens on the nest until a caretaker releases them
• Monitor egg production for each hen• Maintain accurate records for each bird• Hens which produce best kept for continued breeding
Artificial incubator – Allowed for the hatching of large numbers of offspring at the same time
• Precise control incubator environment• Maximizes the number of eggs hatched
Primary Breeder Programs
Primary breeder companies are organized to promote geneticimprovement and multiplication to meet market demands
Pedigree level – Genetic selection occurs at this level, geneticists keep
only the birds that meet specific criteria for continuation of the
pedigree line
Selected pedigree
Unselected pedigreeGreat-Grand Parent level – Mated to
produce Grandparent birds. Still owned by primary breeder company
Grandparent level, mated to produce parent birds. Still owned by primary
breeder company
Parent birds, mated to produce commercial broilers. Breeder company product, birds sold to
integrators
Broiler Level, birds owned by the integrator, birds that are raised and sold for meat
Primary Breeder Programs
Primary breeder companies are organized to promote genetic improvement and multiplication to meet market demands
Ped.
GP
Parent
Commercial Broiler
GGP
1 male, 10 female
150 chicks
6,000 chicks
240,000 chicks
28,800,000 chicks$0.15/chick
$1.50/chick
$15/chick
$150/chick
$1,500/chick
Primary Breeder Programs
Pedigree lines are crossed at the grandparent level**
• Resulting bird is a mixture of the male and female line
• Crossing the pedigree lines results in hybrid vigor
• Hybrid vigor – Crossing of lines producing heterosis
• specific traits in the offspring (GPs) are improved relative to the sire and dam (GGPs).
**This also provides protection of the pedigree line; by purchasing parent birds someone would not be able to re-create
pedigree line
Pedigree
Learning Evaluation
What was the primary reason for moving away from dual purpose birds toward birds bred specifically for egg or meat production?
Meat and egg production are negatively correlated attributes. Therefore a bird that produces meat more efficiently will produce
fewer eggs and vice versa.
Learning Evaluation
How does heritability affect genetic progress?
Traits with high heritability are passed very well from parents to offspring, allowing for large genetic advances to be made with
each generation. Therefore, rapid genetic progress can be made when breeding for traits with high heritability, whereas traits with
low heritability require more generations to improve
Learning Evaluation
Increased selection pressure results in greater or lesser genetic improvements with each generation?
Greater
Learning Evaluation
Critical Thinking
Several traits can be selected for genetic improvement of commercial poultry. Some of these could include:
• Increase of 28 hatching eggs per breeder hen
•2.2% increase in livability of broilers
• Extra 0.4 pounds of broiler body weight without increasing grow-out time
All of these would provide the same financial benefit as selecting for improved breast meat yield. Why then was breast meat yield
selected to improve upon by poultry geneticist?
Breast meat yield improvement is a highly heritable trait, more so than the other traits mentioned