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 Four and Five-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.)