Animal Breeding Systems

advertisement
Animal Breeding Systems
Animal Science II
Chapter 12
Objectives
• Name and explain common breeding
systems used in livestock production
• Explain the effects, advantages and
disadvantages of using various breeding
systems
• Indentify the factors involved in selecting
a breeding system
• Calculate the percentage of parental stock
in offspring using various breeding systems
Systems of Breeding
• 2 basic
– Straight breeding
• Mating animals of the same breed
• Variations-purebred, inbreeding, outcrossing,
grading up
– Cross breeding
• Mating animals of different breeds
• Variations-two-breed cross, three-breed cross,
rotation
Purebred Breeding
•
•
•
•
•
•
An animal of a particular breed
Both parents are purebred
Characteristics of the breed
Eligible for registry in breed association
Tend to be genetically homozygous
Specialized business
Inbreeding
• Mating related animals
• Linebreeding and Closebreeding refer to
how closely related the animals are
• Requires a careful program of selection
and culling
• Expensive
• Used most often by Universities for
experimental work and Seedstock
producers that provide animals for
crossbreeding herds
Closebreeding
• Most intensive
• Animals are very closely related and can
be traced back to more than 1 common
ancestor
• Examples:
– Sire to daughter
– Son to dam
– Brother to sister
Example
1st Mating
A (Male)
B (Female)
1st Generation
½A½B
2nd Mating
A
1/2A 1/2B
2nd Generation
3/4A 1/4B
The offspring of the 2nd generation have received 75% of their genetic make-up from the sire A because he appears closer in
the pedigree to the offspring than he does in linebreeding. They have received only 25% of their genetic inheritance from
the female B.
Linebreeding
• Mating animals that are more distantly related
• Can be traced back to 1 common ancestor
• Examples
– Cousins
– Grandparents to grand offspring
– Half-brother to half-sister
• Increases genetic purity
• Several generations results in desirable and
undesirable genes to become grouped together
with greater frequency—making culling easier
Example
1st Mating
AxB
AxC
1st Generation
½A½B
½A½C
2nd Mating
1/2A1/2 B x 1/2A/2C
2nd Generation
½A¼B¼C
The offspring in the second generation have received 50% of their genetic inheritance from the sire A because he appears
twice in their pedigree. They have received only 25% of their genetic inheritance from each of the females B and C.
Outcrossing
• Mating of animals of different families within
the same breed
• Animals are not closely related
• Purpose is to bring into the breeding program
traits that are desirable but not present in the
original animals
• Used most by purebred breeders
• Popular because it reduces the chances of
undeniable traits are still present
• Sometimes used in inbreeding programs to
bring in needed traits
Linecrossing
• Mating animals from two different lines
of breeding within a breed
• Purpose is to bring together desirable
traits from different lines
• Experience is the best guide to use
when line crossing
Grading Up
•
•
•
•
Mating purebred males to grade females
Good way to improve quality
Less expensive
Use of purebred sires long enough will
eventually lead to the amount of grade
breeding left in the offspring being less
than 1%
Example
1st Mating
AxG
1
1st Generation
1/2A11/2G
50% Pure 50% Grade
2nd Mating
A2 x ½ A1 ½ G
2nd Generation
½ A2 ¼ A1 ¼ G
75% Purebred, 25% Grade
3rd Mating
A3 x ½ A2 ¼ A1 ¼ G
3rd Generation
½A3 ¼A2 1/8A1 1/8G
87.5% Purebred, 12.5% Grade
Crossbreeding (X)
• Mating two animals of different breeds
• Offspring is a Hybrid
• Usually results in improved traits
because dominant genes mask
undesirable recessive genes
• Superior traits that result from
crossbreeding are called hybrid vigor or
heterosis
General Considerations Regarding
Beef Crossbreeding Systems
• Good record keeping is essential
• Calving difficulties may increase when crossing
large breed sires with small breed dams
• Fewer calving problems if large breed dams are
used
• Large breed dams have higher maintenance
costs
• Artificial insemination allows access to better
bulls
• To avoid inbreeding more than 1 breeding
pasture may be required
Beef Crossbreeding Systems
•
•
•
•
•
•
•
•
Terminal Sire Crossed with F1 Females
Rotate Herd Bull every 3-4 years
Two Breed Rotation
Three Breed Rotation
Four and Five Breed Rotation
Static Terminal Sire
Rotational Terminal Sire
Composite Systems
Terminal Sire Crossed with F1
Females
• Replacement crossbred (F1) females in
the herd are purchased and crossed
with a terminal bull.
• All offspring are sold.
Rotate Herd Bull Every 3-4 Years
• Same breed of bull is used for several
years and then replaced with a bull of a
different breed.
• Replacement females are selected from
the herd.
Two-Breed Rotation
• Bulls from Breed A are crossed with cows
from Breed B.
• Resulting heifers are bred to bulls from
breed B for the duration of their
productive life.
• Replacement heifers from that cross are
bred to bulls from breed A.
• Each succeeding generation of replacement
heifers is bred to a bull from the opposite
breed used to sire the replacement heifer.
3 Breed Rotation
• Same pattern of breeding as the 2
breed rotation except that a bull from a
3rd breed is used in the sire rotation.
4 and 5 Breed Rotations
• Larger herds
• Bulls from a 4th or 5th breed may be
used in the rotation of sires
• This system requires a higher level of
management and record keeping than 2
and 3 breed systems.
Static Terminal Sire System
• 4 breeding groups
• Group 1 (25% of the herd) mates breed A bulls to breed A cows
to produce replacement heifers for group 1 and group 2.
• Group 2 (25% of the herd) breeds the AA heifers to a bull
(breed B) to a different breed, producing crossbred heifers
(breed AB)
• Group 3 (50% of the herd) breeds the AB heifers to a terminal
(T) bull selected for its ability to transmit a high rate of gain.
• A subgroup (Group 4, 10% of the herd) of the 3rd group is
composed of AB heifers being bred for the first time. These AB
heifers are bred to a smaller breed (breed C) bull to reduce 1st
time calving problems.
• All the male offspring of groups 1 and 2 and all offspring of
groups 3 and 4 are sold.
• Any heifers from groups 1 and 2 that are not kept for breeding
are also sold.
Rotational –Terminal Sire System
• Two breeding groups needed
• Bulls from breeds A and B are used on a
rotating basis on 50% of the herd
providing crossbred females for the entire
herd
• Mature cows in the herd are mated with a
terminal bull to produce offspring, all of
which are sold.
• Replacement females come from mating of
bulls A and B with younger cows in the
herd.
Composite Breeds
• Developing a new breed based on
crossbreeding 4 or more existing
breeds of cattle to avoid inbreeding
problems
• After development the composite breed
is not crossbreed with other breeds
Composite Breeds
Noble Line Bull ¾ Gelbvieh, 1/3 Angus, 1/3 Brahman
Composite Breeds
Leachman Stabalizer Cow
1/2 British: 1/2 Continental composite 1/4 Red
Angus:1/4Hereford: 1/4 Gelbvieh: 1/4 Simmental
Composite Breeds
Leachman Range Maker Bull
3/4 British: 1/4 Continental A blend of Red Angus and Black Angus,
South Devon, and Tarentaise (and/or Salers)
Crossbreeding Systems for Swine
• Rotational Crossbreeding
• Terminal Crossing System
• Rotaterminal System
Crossbreeding Systems for
Sheep
• Rotational
• Static
• Rotostatic
Summary
• 2 basic breeding systems—straight and crossbreeding
• The type of system used depends on: the size of the operation,
the amount of money available and the goal of the producer
• Purebred animal are eligible for registry and tend to be
genetically homozygous
• Inbreeding increases the genetic purity of livestock but
generally reduces performance. It is not generally used by the
average producer but rather by those that do experimental
work to improve the breed.
• Outcrossing brings genetic traits into the breeding program
that tend to hide undesirable traits
• Crossbreeding is the mating of animals from two different
breeds, it is used by many commercial producers and usually
results in hybrid vigor. This improves some traits but all little
effect on feed efficiency and carcass traits.
Download
Related flashcards

RNA

23 cards

Chromosomes

11 cards

Epigenetics

15 cards

Phylogenetics

19 cards

Medical genetics

17 cards

Create Flashcards