Poultry GeneticsPoultry Genetics AgScience Poultry Science Curriculum Section 2 Historical Overview...

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Poultry Genetics AgScience Poultry Science Curriculum Section 2

Transcript of Poultry GeneticsPoultry Genetics AgScience Poultry Science Curriculum Section 2 Historical Overview...

Poultry Genetics

AgScience Poultry Science Curriculum

Section 2

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