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In poultry keeping, yarding is the practice of providing the poultry with a fenced yard in addition to a poultry house. Movable yarding is a form of managed intensive grazing. Yarding is often confused with free range. The distinction is that free-range poultry are either totally unfenced, or the fence is so distant that it has little influence on their freedom of movement. == Historical practice == Before the discovery of vitamins A and D in the 1920s, green feed and sunshine were essential to the health of poultry. Vitamin D was synthesized from sunlight on the skin (as with humans), while Vitamin A was obtained through green forage plants such as grass. Yards small enough to be fenced economically were soon stripped of palatable green forage and become barren. This is followed by a build-up of manure, parasites, and other pathogens. Free range husbandry was the most common method in these early days. Most farms had only a small free-range barnyard flock. Larger flocks were kept in small houses build on skids, which were dragged periodically to a fresh piece of ground. This method is similar to the modern practice of pastured poultry. Experts of the day estimated the sustainable level to be about fifty hens per acre (80 m² per hen), with one hundred hens per acre (40 m² per hen) as an absolute upper limit if special care was taken. These levels are sustainable in the sense that the turf can make use of the nutrients in the manure left behind by the chickens, and in the sense that, at this stocking density, the chickens will not completely destroy the turf through scratching.
Because fifty hens per acre represents per hen (80 m² per hen), while the density inside the house at the time was normally four square feet per hen (0.4 m² per hen), this required that the yard be 200 times wider than the house, assuming a yard on one side of the house. That is, a house wide required a yard wide to provide the necessary area. This would normally be provided as two yards, one on either side of the house, each wide. In reality, such yards are expensive to fence, and the chickens spend most of their time on the portion closest to the house, so sustainability was never achieved in practice except with portable houses, which were moved periodically to fresh ground. Yarded operations were operated with unsustainably small yards that were quickly denuded and which received excessive levels of manure. The use of multiple yards, frequent plowing, and liberal use of lime would allow higher stocking levels to be used, since plowing and liming would allow much of the nitrogen to escape from the soil. The following is typical advice for the successful use of yards in the Thirties and Forties:
Nutritional advances increasingly turned yarding into a liability, and it fell out of favor. Free range continued to be used, especially for breeding flocks and for pullets before they reached laying age, because of the lower rate of disease and greater overall health of grass-reared chickens. Breeding flocks (which lay eggs destined for incubation) are always given a better diet than flocks laying table eggs, since a diet that will produce table eggs cheaply will not provide eggs that hatch well. For some time after confined laying flocks produced table eggs satisfactorily, breeding flocks benefited from free range In Britain, Geoffrey Sykes developed a new yarding system in the Fifties.〔Geoffrey Sykes, The Henyard. 1952. Crosby Lockwood & Sons.〕 This used a small yard covered with a thick layer of straw, with more straw added frequently. He also recommended that shade and a windbreak be provided by a solid fence around the yard, or by other means, such as rows of haybales. Once a year, the old straw was removed by a front-end loader or similar machinery. This method eliminated mud and pathogens. It was later forgotten because the industry moved to high-density confinement before the method was widely established. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yarding」の詳細全文を読む スポンサード リンク
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