1. Assisted Reproductive Technology
Since animals were first domesticated, many technologies have been developed to select for desirable qualities, make breeding easier, and make animals produce more offspring.
Many of those technologies, including artificial insemination, in vitro fertilization (IVF), embryo flushing, and cloning, involve the manipulation of animal reproduction.

2. Artificial Insemination
History of artificial insemination

Artificial insemination refers to the introduction of semen and viable sperm into the female reproductive tract via artificial means. Lazzaro & Spallanzani, a French physiologist, was the first person to successfully demonstrate artificial insemination in animals, when he artificially impregnated a dog in However, the use of artificial insemination for commercial purposes began in 1937, when the first artificial insemination cooperative was established in the US. Artificial insemination is still widely practiced today; approximately 60% of dairy cows in the US are bred by artificial insemination.

3. Spermatozoa extraction and storage
Although many different animals require different methods of artificial insemination, the basic premises remain the same. First semen must be extracted from the male. There are a variety of extraction techniques; however, most often a mechanical breeding mount containing an artificial vagina is used. In the case of dairy cattle, the bull is allowed to first mount a live cow, which is known as the teaser animal.
The bull is allowed to repeatedly mount the teaser animal without ejaculating. After a few live mounts, the bull is now directed to an artificial vagina and ejaculation is allowed to take place. The teaser animal serves to increase the amount of viable sperm per ejaculation.

4. After ejaculation, the sperm is collected and sperm sorting may be applied. The sperm is sorted into a male and female population by a flow cytometer, and is typically 90–98% accurate for most breeding species. Sperm sorting is primarily reserved for industries where one sex is more valuable, such as the dairy industry where females are required for milk production. Because one ejaculation contains exponentially more sperm than is necessary for fertilization, an extender solution is added to the semen for dilution and freezing purposes. Depending on the fate of the semen, the extender can be composed of a variety of ingredients.

5. Extenders typically contain milk or egg yolk to protect against cold shock, cryo-protectants such as glycerol, buffers to protect against pH changes, and energy sources for the sperm such as glucose. It is also common for extenders to contain antibiotics to protect against contamination. Once the extender is added to the semen, the semen is frozen down in multiple plastic tubes known as straws. The straws are stored in liquid nitrogen at −196 °C until they are needed for insemination. These advances in cryopreservation of semen have greatly advanced the practice and prevalence of artificial insemination.