The use of frozen semen to impregnate animals and in particular horses is a global business. Also known as artificial insemination, this practise goes beyond farming and is widely used among breeders of racing animals in order to maintain and expand the bloodline of an animal with desirable traits.
Although ancient Arabian texts describe the successful artificial insemination of mares, the use of frozen semen is relatively new as previous societies lacked the technology to freeze and store semen. It wasn't until the early 20th century that the practice was used in the mainstream and initially began in Russia, where stud farms were reported as freezing and storing semen using snow. However this way of doing it is risky and would likely fail on many occasions making it inefficient. Nowadays it's used regularly in the western world as we have the equipment to do it successfully and safely although it still has its critics in regards to ethics of the practice. It has become so common that regulations have had to be put in place to protect the animals as well as the breeders.
In the 18th century it was realised that placing spermatozoa in a cold or freezing environment would not necessarily kill it, if done fast enough. It leaves the sperm inactive and preserved, and once warmed they become active once more. Once more however this must be done correctly as heating to fast will damage or destroy the cells. Once collected the semen must be kept at -320 Fahrenheit and at this temperature there is currently no know maximum amount of time that it can be kept.
The biggest appeal of this practice is amount of money saved by breeders. It's a lot cheaper to transport just the frozen sperm to breed with a mare than it is to transport the horse itself.
It is also popular among breeders as it allows for the DNA of prize horses with desirable attributes to be saved long after the death of that horse. In addition to this it allows farms and breeders to add to their income relatively consistently.
One major issue is the specialty equipment required for the process, leaving breeders with a hefty upfront fee making it less viable for smaller breeders. Perhaps the biggest issue is the ethical concerns that surround it. Freezing of sperm of any animals with the intention to later impregnate another is seen by some animal rights activists as cruel and as "playing God".