Animal Husbandry is a branch of agriculture concerned with the domestication of, care for and breeding of animals such as dogs, cattle, horses, sheep, goats, pigs and other like creatures. Animal husbandry began in the Neolithic around 10,000 years ago.
Selective Breeding of animals with good physical attributes helps making your animals more effective. For example cows give way more milk now than 1000 years ago. Another example of selective breeding is the Irish Hobby it was breed in Ireland prior the 13th Century. The breed is ancestor of many modern horse breeds. It was designed to be small, agile and light. It was used during the scottish war of independence by both sides for light cavalry also known as Hobelars.

Sources: wikipedia, ancient.eu.com and infoplease.com