Selective breeding of cattle has occurred for centuries, as farmers breed cattle to emphasise certain attributes. Farmers selectively breed cattle by specifically causing two animals with favourable attributes to mate. Farmers may even use artificial insemination to ensure the cows breed. Over several generations, farmers hope to create a breed of cattle that all have these desired attributes. Farmers may breed cattle for their meat, dairy production or even for aggressiveness.
The Belgian blue is a classic example of a species selectively bred for beef production. Belgian blue cattle have a specific gene mutation that promotes muscle growth. Belgian blue cattle, then, produce substantially more meat than many other types of cattle, and can grow to very large sizes. In fact, Belgian blue calves are so large that they typically must be taken from their mother's womb by caesarean section rather than naturally.
Many breeds exist that emphasise dairy production. In fact, selective breeding of cattle for dairy production has become so specialised that farmers can predict the fat and protein content of the milk based on the breed of the cow. The Holstein breed of cow, with its famous black and white spots, can produce up to 3,260 gallons of milk per milk cycle of 305 days, which works out to more than 10 gallons of milk a day.
The highland cattle breed of Scotland is the world's oldest registered breed of cattle, and was officially established in 1884. Rather than promote dairy or beef production, the highland cattle has been bred to preserve the natural characteristics of wild cattle. Its hardy nature, minimal maintenance requirements and resistence to disease make it a popular choice for selective breeders to incorporate into their lines. While the highland breed was not bred with beef production in mind, the contemporary demand for lean, lowfat meat has made the highland breed, which has very little fat content relative to other breeds, increasingly popular.
The Spanish sport of bullfighting requires an aggressive, combative bull. Therefore, Spanish herders have bred the Spanish fighting bull specifically to emphasise aggression. This bull, often lean, muscular and a dark brown or black colour, is consistently combative in bullfighting rings. Because it is not bred for beef production, it is much faster and smaller than other types of bulls.