Transcript Animal Science Unit 2b: Animal Breeding

Animal
Reproduction
Animal Science
Definitions
Purebred (straight breeding): the mating of
animals from the same breed.
Crossbreeding: the mating of animals from
two or more different breeds.
Definitions
• Homozygous-two parental genes calling
for a specific characteristic that are
identical
• Heterozygous-two parental genes calling
for a specific characteristic that are not
identical. (The dominant gene will override
the effect of the recessive gene.)
Purebred
Advantages:
- Ancestry is known back to the start of the
breed.
- genetically homozygous
- The foundation stock of crossbreeding.
Purebred
Disadvantages:
- Undesirable traits are more concentrated
because of the homozygous genes.
- Very expensive to start.
- Must market to get full value of animal.
Crossbred
Advantages of Crossbreeding
- Used to improve genetics.
- Dominant genes mask recessive genes.
- Hybrid vigor, or heterosis, occurs from the
combination of genes.
- Cheaper to get started.
Crossbreed
Disadvantages of Crossbreeding
- Often lack superior genes of purebreds.
- Must settle for market value at sale barn.
BREEDING SCHEMES
Inbreeding: Mating of related animals
- close breeding: animals being mated are
very closely related and can be traced
back to more than 1common ancestor.
i.e. Father and daughter
- most intensive form
- high presence of undesirable traits
BREEDNG SCHEMES
Line breeding: mating of animals that are
more distantly related and can be traced
back to one common ancestor.
i.e. Cousin, grandparent to grand
offspring, half-brother to half-sister.
BREEDING SCHEMS
Out crossing: the mating of animals of
different families within the same breed.
• Animals are not closely related
• Purpose is to introduce new, desirable
genes into the breeding program.
• Reduces the changes of recessive genes
appearing.
• Most popular method of pure breeding.
BREEDING SCHEMES
• Grading up: the mating of a purebred sire
to grade females.
• Grade animal is any animal not eligible for
registry.
• Cheap method of improving the herd
• Only one purebred sire is needed or
artificial insemination can be done.
• Improves the quality of the herd very
quickly.
BREEDING SCHEMES
• Two-breed rotation
– Bulls from breed A are crossed with Cows from breed
B.
– The resulting heifers are bred to bulls from breed B
for the duration of their productive life.
– Replacement heifers chosen from these meetings are
bred to bulls from 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.
BREEDING SCHEMES
• Three-breed rotation
– The pattern of breeding is the same as in a
two-breed system, except that a bull from a
third breed is used in the rotation of sires.
• Four and Five-breed rotation:
– Used in large herds
– A fourth of fifth bull is added to the system
– Requires intense management practices.
Terminal Cross System
• Cross is made that the offspring are
undesirable for breeding.
• Ex. Smut face lamb (Black faced male on
white faced female.)