On most farms in the very early 1900`s farms kept one or two bulls to

On most farms in the very early 1900’s farms kept one or two bulls to
inseminate their whole herd. Farmers would personally take the bulls
out to pasture with the cow in heat and advise the process. At that time
farmers were unaware of inbreeding the diseases associated with it
causing many casualties in their herds. Unlike today, farmers worried
solely about their cows producing milk and bred for that purpose and
that purpose alone.
In the 1930’s the Holstein Association sent out letters to farmers around
the country asking them to track their bulls and the milk production of
their offspring. The trend of evolution and natural selection was
becoming noticed within the breed and after 5 years of information
gathering from around the country the Holstein Association created bull
records (now called proofs) to help farmers breed according to the bulls
daughters and phenotypes. These records were used by farmers to select
which of their bulls to use on different cows, still unable to get semen
without the bull being at their farm.
The artificial insemination (AI) industry has had a tremendous impact on
genetic improvement of the breed. Since perfection of the semen
freezing process in the late 1940's, AI has allowed the use of superior,
proven bulls by Holstein breeders across the country. Today, AI
accounts for 85 percent of Holstein births. AI made the development of
reliable, unbiased methods to evaluate Holstein genetics possible. With
AI, a single Holstein bull can sire as many as 50,000 daughters. Type and
production information on all these females makes it easier to predict
performance of future offspring and evaluate the quality of genetics
transmitted from sire to offspring.
Genomic Selection is a new technology that helps the dairy
industry evaluate bulls on the basis of their DNA profile,
allowing breeders to predict, among other things, which
animals are going to give higher milk yields in a much shorter
time period than previous methods. Within just the past 5
years researchers have discovered different genetic
components of phenotypic variation that facilitate stable
changes in production, fertility and health through selection.
Genomics are used to breed for milk productions, show cattle,
and bring back lost dominant traits in offspring.