Modern cattle breeding practices today are still based largely on mass selection,
supplemented by three other methods: pedigree selection,family selection, and progeny selection.
Pedigree selection focuses on the quality of the
ancestors rather than of the individual. Pedigree selection is useful in evaluating young animals whose phenotypes
are not fully developed, and in selecting for traits that are known to have high heritability. However, pedigree
selection is a slow process.
Family selection, based on analyzing the qualities of relatives, is
faster. Family selection is often used in conjunction with individual selection, and it is valuable in estimating
sex limited traits in selecting the males from which to breed.
Progeny selection involves selecting individuals based on the records of their progeny.
Like family selection, it is useful when selecting for such sex limited traits as milk yields in the progeny of a
bull and traits with low or uncertain heritability. However, progeny selection is a slow process because it
requires waiting for one generation or more to determine the quality of a given individual's offspring.
Since the mid 18th century, cattle breeders have combined various methods of selection
with inbreeding and outbreeding of stocks.
Inbreeding involves crosses between closely related individuals. To fix or intensify a
particular trait, herds or flocks are subdivided into smaller groups and intensively inbred for several
generations. To increase vigor and avoid the accumulation of unwanted traits, individuals from these inbred stocks
are then outbred, or crossed with members of other stocks.
Outbreeding increases variability and produces new combinations of traits. Increasingly
in the 20th century, as methods for freezing and storing sperm have been perfected, both inbreeding and outbreeding
have been carried out by artificial insemination.
Embryo selection is another method by which the breeder can increase desired traits in
a population. In this method, fertility hormones are given to females that carry selected characteristics. Once the
eggs have been fertilized, they are taken from the selected females and implanted in other females that carry them
through the gestation period and then give birth. Embryo transfer is used less frequently than artificial
insemination because it is more complicated and more expensive.