changes in the value of land due to high prices for cash crops like soybeans. Auctions are a common means of sale, although in some cases, prospective buyers inspect sale cattle on the producer's property with the price negotiated either by weight or on a dollars per head basis. In the United States Cow–calf operations are generally divided into two types. First are those that produce feeder cattle to be raised by other agricultural enterprises, such as feedlots. These sell their calves after they have been weaned and are under a year in age. The second are those that raise the calves for 1–2 years before selling them directly to slaughter. The mother cattle, sometimes known as brood cows, generally come from one of two sources: either female calves raised on the farm itself and retained into adulthood, or cows that are purchased from a specialized seedstock operation which often produces purebred cattle. Cow–calf operations are widespread throughout the United States. A 1997 census found that this sector of the U.S. beef market produced over $40.5 billion. As of 2007 there were more than 765,000 cow–calf operators in the country, mostly concentrated in the Western and Southeastern U.S. states. Sale prices for calves sold from a cow–calf operation are subject to fluctuation as part of the cattle cycle of financial markets. The relatively long period it takes a cow–calf operator to build up a beef herd and raise new calves to the desired weigh tends to extend the length of such a cycle. In Australia Approximately 90% of Australian cows are in strictly cow–calf operations. In southern Australia (NSW, Victoria, Tasmania, South Australia and south-western Western Australia) beef cattle are often reared on smaller properties as part of a mixed farming or grazing operation, but some properties do specialise in cattle breeding. The southern calves are typically reared on pasture and sold as weaners, yearlings or as steers at about two years old or older. In the Top End, sub-tropical areas and in arid inland regions cattle are bred on native pastures on expansive cattle stations. Beef producers in northern Australia tend to operate more extensive pastoral enterprises than counterparts in southern Australia. Anna Creek Station in South Australia, Australia is the world's largest working cattle station. The North Australian Pastoral Company Pty Limited (NAPCO) is now one of Australia's largest beef cattle producers, with a herd of over 180,000