Presentation on theme: "Animal Breeding Systems Animal Science II Chapter 12."— Presentation transcript:
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 The offspring of the 2 nd 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. 2 nd Generation 3/4A 1/4B 2 nd Mating A1/2A 1/2B 1 st Generation ½ A ½ B 1 st Mating A (Male)B (Female)
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 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. 2 nd Generation ½ A ¼ B ¼ C 2 nd Mating 1/2A1/2 B x 1/2A/2C 1 st Generation ½ A ½ B½ A ½ C 1 st Mating A x BA x 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 3 rd Generation ½A 3 ¼A 2 1/8A 1 1/8G87.5% Purebred, 12.5% Grade 3 rd Mating A 3 x ½ A 2 ¼ A 1 ¼ G 2 nd Generation ½ A 2 ¼ A 1 ¼ G75% Purebred, 25% Grade 2 nd Mating A 2 x ½ A 1 ½ G 1 st Generation 1/2A 1 1/2G50% Pure 50% Grade 1 st Mating A 1 x G
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 F 1 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 F 1 Females Replacement crossbred (F 1 ) 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 3 rd breed is used in the sire rotation.
4 and 5 Breed Rotations Larger herds Bulls from a 4 th or 5 th 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 3 rd 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 1 st 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 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.