are shorn once a year, most often in the spring. The average weight of the fleece is . The wool is medium to coarse: staple length is about and fibre diameter about (Bradford count ). In general, the fleece is light, soft, springy and open, with little lanolin (grease); there may be some kemp. In some sheep (particularly British Jacobs, which have denser fleeces), the black wool grows longer or shorter than the white wool. This is called "quilted fleece", and is an undesirable trait. While other British and Northern European multi-horned sheep have a fine inner coat and a coarse, longer outer coat, Jacobs have a medium grade fleece and no outer coat. Lambs of the more primitive lines are born with a coat of guard hair that is protective against rain and cold; this birth coat is shed at 3–6 months. Some individual sheep may develop a natural "break", or marked thinning, of the fleece in springtime, which can lead to a natural shedding of the fleece, particularly around the neck and shoulders. The medium-fine grade wool has a high lustre, and is highly sought after by handspinners if it is free of kemp. The colours may be separated or blended after shearing and before spinning to produce various shades of yarn from a single fleece, from nearly white to nearly black. Tanned Jacob sheepskins also command high market prices. References Further reading L. Heise & C. Christman (1989). American Minor Breeds Notebook. Pittsboro, North Carolina: The American Minor Breeds Conservancy. Ólafur R. Dýrmundsson & Roman Niznikowski, (2008). "North European short-tailed breeds of sheep: a review. 2008 Annual Meeting of the European Federation for Animal Science. Vilnius, Lithuania: EAAP Sheep and Goat Commission: 1–24. M. L. Ryder (2007). Sheep and Man. London: Gerald Duckworth & Company. . P. Simmons & Carol Ekarius (2009). Storey's Guide to Raising Sheep. North Adams, Massachusetts: Storey Publishing. . External links American Jacob Sheep Registry Jacob Sheep Breeder's Association Jacob Sheep Conservancy Jacob Sheep Society Conservation Priority Breeds of the Livestock Conservancy Sheep breeds originating in England