Dairy cattle, generally of the species Bos taurus, are domesticated animals bred to produce large quantities of milk.

Terminology

A young dairy animal is known as a calf. A female calf which has not given birth to a calf and is less than thirty months old is called a heifer. When the heifer has reached the stage in pregnancy where the udder starts to swell, it is known as a springer. After calving, or when more than thirty months old, a female dairy animal is known as a cow. The process of birthing a calf is known as calving or partuition. A male dairy animal is called a bull at any stage of life, unless castrated, in which case it is known as a steer until it is four years old, then it is called an ox. A dairy animal's mother is known as its dam. Similarly, a dairy animal's father is known as its sire.

Modern Times

Dairy cattle are now specialized animals, focused primarily on producing milk. This milk is made into various products, including cheese, yogurt, butter, ghee, cottage cheese, and ice cream, and is consumed around the world.

Dairy Farms

Cattle on a dairy farm in Maryland, United States.

Dairy cattle may be found in herds on farms where dairy farmers own, manage, care for, and collect milk from them. These herds range in size from small boutiques of fewer than five cows to large conglomerates of 25,000 cows or more. The average dairy farmer in the United States owns about one hundred cows and is about 53 years old.

Life of dairy cattle

Dairy cattle are distinguished by sex at birth. Cows are unique in their ability to produce milk, and thus heifers, young cows, are generally considered more valuable than bulls, which are used solely for beef production and breeding purposes.

Most dairy calves are separated from their dams within a few hours of birth. Such separation ensures decreased risk of disease passing from dam to calf and also allows the dam to begin producing milk for human consumption as soon as possible. The dam's first milk, called colostrum, is rich with antibodies and immune factors, is required for newborn calves to survive, although it is unfit for human consumption. A calf must drink two quarts (2 L) of colostrum within twelve hours of birth or its future may be in jeopardy, as a newborn calf has no immune system of its own and must rely on maternal antibodies contained in the colostrum for protection. The dam's milk quickly changes into that most suitable to humans, and within three days after calving, a cow's milk is already on its way to human hands. Most young stock then subsist on milk replacer, a commercial feed additive used to take the place of the cow's natural milk, until old enough to consume more solid foods.

The bull

In New Zealand and some other countries male calves are slaughtered at two to four days for their abomasum (fourth stomach), rennet and for veal.

In Europe and North America most newborn dairy bulls will be slaughtered for veal before reaching six weeks of age. Many bulls, however, will be raised as steers and butchered for dairy-beef when about eighteen months old.

A select few high-quality bulls, however, will be raised for breeding purposes. These bulls will generally have excellent conformation, or type (for the breed), outstanding pedigrees and, early in their breeding life, produce progeny that is superior in dairy production.

Herd bulls, or bulls that live with dairy cows and provide direct, natural breeding, will service up to one hundred fifty cows at any given time. Such a bull will be used in one herd for up to two years before the risk of inbreeding and the bull's increasingly hostile temperament forces a farmer to move the bull to a new herd.

More recently, since the 1950s, artificial insemination has become the way of the dairy cow. Through artificial insemination, fewer than a thousand elite bulls serve as sires for entire generations of calves. Although conception is dependent upon effective herd management and heat detection which increase the time the dairy farmer must spend with the cows, a few factors have prompted farmers to use artificial insemination nearly exclusively. The foremost contributor is the high quality of calves produced through artificial insemination. Artificial insemination also limits the need for farmers to maintain their own bulls, which contributes to safety, as bulls can be dangerous animals to keep on the farm. Some dairy farms, however, still use live bulls, as it is easier to maintain a few bulls than implement the extensive herd management requirements to use artificial insemination effectively.

The cow

Dairy cows being fed

Dairy heifers are treated most generously by farmers, as the heifers form the farmer's future herd of cows. As a cow cannot produce milk until after calving (giving birth), most farmers will attempt to breed heifers as soon as they are fit, at about fifteen months of age. A cow's gestation period is about nine months (279 days long), so most heifers give birth and become cows at about two years of age.

A cow will produce large amounts of milk over its lifetime. Certain breeds, of course, produce more milk than others; however, each breed normally used in dairy production ranges from 8,000 to 12,700 kg (18,000 to 28,000 pounds) of milk per annum. The average for milk cows in the US in 2005 was 8,800 kg (19,576 pounds). The process of milking the cow is essential for the cow's survival. If the cow is not milked properly the pressure will build inside the udder causing it to explode.

About 70 days after calving, a cow's milk production will peak. The cow is then bred. The cow's production slowly dwindles until, at about 305 days after calving, the cow is 'dried', when the farmer stops milking her. About sixty days later, one year after her previous calf was born, a cow will give birth again.

Alternatively, farms may choose to forego this cycle, and settle for the lower production rate of perennial cows. A survey performed by DHI Computing Service in Utah, found that average production had dropped to 21.6 kg/day (corresponds to 7,900 kg/year) after four years of continuous milking.

When kept inside year-round most dairy cows live to be five or six years old before their annual milk production decreases to the point where it is no longer profitable for a farmer to keep them. Grazing cows will not produce as much milk; however, they will likely have a longer lifetime, up to 12 years depending on production that is measured monthly, because a farmer who grazes his cattle will generally retain cows that produce less milk than cows owned by farmers who raise cattle in barns. At death, the cow is butchered and sold for its meat.

More recently, certain practices have been enacted to ensure that high quality cows' progeny is more widespread than what is naturally possible. Some cows are 'flushed', where 7-12 embryos are removed from their reproductive systems. These embryos are then transferred into other cows who serve as surrogate mothers. This process is called an 'embryo transfer'.

Breeds

Exotic dairy cattle are divided into six major breeds. These are the: Holstein-Friesian, Brown Swiss, Guernsey, Ayrshire, Jersey, Sahiwal and Milking Shorthorn. Other dairy breeds include Danish Red, Red Sindhi, Butana, Illawarra, etc.

References

• Robert D. Moore: The Carnation Milk Farms: Home of Contented Cows
• US Department of Agriculture: Milk Production, Disposition, and Income Annual Summary
• C. A. Rotz, et al: Economic and Environmental Feasibility of a Perennial Cow Dairy Farm

Wikipedia

http://en.wikipedia.org/w/index.php?title=Dairy_cattle&action=history

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