Polled Dorset
| Polled Dorset | |
|---|---|
 | |
| A photo of a ewe and lamb taken at the North Carolina State University Small Ruminant Unit. | |
| Conservation status | |
| Domesticated | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | Bovidae |
| Subfamily: | Caprinae |
| Genus: | Ovis |
| Species: | O. aries |
| Binomial name | |
| Ovis aries Linnaeus, 1758 | |
The Polled Dorset is a breed of sheep developed for meat at the North Carolina State University Small Ruminant Unit in 1956. The name refers to the fact that it is a hornless variation of the Horned Dorset breed. The Polled Dorset is the result of a genetic mutation by which some of the offspring of a certain ram grew no horns. After some years of breeding work, a strain of Dorset was developed which had lost the characteristic horns and which bred true.
Polled Dorsets are an all-white, medium-sized sheep, prolific and able to breed out of season. The carcases are muscular with good conformation and the adults produce a thick fleece, which is free from dark fibers. Since its development, the number of Polled Dorsets registered in the United States has grown to exceed the number of Horned Dorsets. Without horns the sheep are easier to handle and there is much less risk of the rams hurting themselves or others by butting. The Polled Dorset is sometimes confused with the Australian Poll Dorset, but that breed did not start as a genetic mutation but resulted from the introduction of Corriedale and Ryeland blood into the Dorset breeding program.
History
In 1949, four hornless lambs were sired from a Horned Dorset on a farm at North Carolina State University in Raleigh, North Carolina. Over the next five years, as part of their normal breeding program, those four ewes and the other ewes on the farm were bred to the Horned Dorset. Eventually, a ewe gave birth to twin rams. NCSU 401 was a regular horned Dorset, but his brother, "NCSU 402", was born polled, without horns, due to a genetic mutation. Thus, the Polled Dorset was born.[1] NCSU 402 was the official name given to the first true Polled Dorset sheep. It was named in accordance with the naming system that has been used at the NCSU Small Ruminant Unit since it started its breeding program.
After research and testing were done to confirm that the Polled Dorset carried the same characteristics as the Horned Dorset and was able to pass on these traits, the Continental Dorset Club, formed in 1898, registered the very first Polled Dorset sheep in 1956.[2][3] Livestock scientists, the late Dr. Lemuel Goode and the late Sam Buchanan, are credited with identifying and developing the hornless sheep. The offspring of NCSU 402 were bought by other breeders and within twenty years, seventy percent of all registered Dorsets were polled. The success of the Polled Dorset has made it considered to be the second most popular sheep breed in the United States.[1] A polled strain of Dorsets were also developed in Australia in the 1900s,[3] however, these were not as a result of a genetic mutation but resulted from the introduction of Corriedale and Ryeland blood into the Dorset Horn.[2]
Conformation
Polled Dorsets are a medium-sized sheep that are long lived and prolific, heavy milkers. They produce hardy lambs with moderate growth and maturity that yield heavily muscled carcasses.[4] Their fleece is very white, strong, close, free from dark fiber and extends down the legs. When shorn, fleece averages between five and nine pounds (2.23 to 4 kg) in ewes and fifty to seventy percent of their fleece can be used.[5] The staple length ranges from 2.5 to 4 inches (6 to 10 cm) with a numeric count of 46's-58's. The fiber diameter ranges from 27.0 to 33.0 microns. At maturity, ewes weigh between 150 and 200 pounds (67 to 91 kg), some weighing more in show condition. Mature rams range in weight from 225 to 275 pounds (102 to 125 kg). Dorsets are noted for their ability to be bred more than once per year and are commonly used in crossbreeding to produce females for out-of-season breeding.[4] They are one of the few breeds that have this characteristic. Multiple births are common and they work well in commercial operations, including programs where rams are specifically used to sire lambs for slaughter. These rams are known as terminal sires since their genetics are more suitable for slaughter than breeding purposes.[5]
Since the breed first became commercial, it has spread to Canada and become a major contributor in the commercial lamb industry. The breed adapts well to confinement and is readily used in accelerated crossbreeding programs. Polled Dorsets thrive under grass-based and feedlot conditions and are more suitable on small farms that are intensely managed.[6]
Polled versus Horned Dorsets
The Dorset is an ancient breed that was most likely developed from horned sheep that lived in the valleys and pastures of southwestern England. Dorset Horn sheep were imported into the United States in 1860, and the first U.S. national flock book was formed in 1891.[7] Today, the Dorset is found in two varieties globally, Horned and Polled. In the Horn variety, both ewes and rams have horns, while the polled variety have no horns at all. Polled Dorsets are ideal for commercial settings because they do not have horns that can get caught in fencing or cause damage when they butt.[2]
Polled Dorsets are the most popular white-faced breed in North America, while the much less-common Dorset Horn is listed as "threatened" by The Livestock Conservancy in the United States.[2] In essence, the difference between the two breeds is that one has horns and the other does not.[8]
References
- ↑ 1.0 1.1 "Monument dedicated to sheep, scientists". Perspectives: The Magazine of the College of Agriculture and Life Sciences 1 (1). Winter 1999.
- ↑ 2.0 2.1 2.2 2.3 "Dorset Horn Sheep", livestockconservancy.org (The Livestock Conservancy), retrieved 2013-09-02
- ↑ 3.0 3.1 Carol Ekarius (2008), Storey's Illustrated Breed Guide to Sheep, Goats, Cattle and Pigs: 163 Breeds from Common to Rare, Storey Pub., pp. 236–237, ISBN 978-1-60342-036-5
- ↑ 4.0 4.1 "Meat Breeds: Dorset (Polled and Horned)". American Sheep Industry Association. Retrieved May 30, 2013.
- ↑ 5.0 5.1 "Dorsets Horned and Polled". Oklahoma State University Department of Animal Science. Retrieved May 30, 2013.
- ↑ "Polled Dorset". Canadian Cooperative Wool Growers. Retrieved May 30, 2013.
- ↑ Janet Vorwald Dohner (2001), The Encyclopedia of Historic and Endangered Livestock and Poultry Breeds, Yale University Press, pp. 108–110, ISBN 978-0-300-13813-9
- ↑ "Dorset Horn". SVF Foundation. May 30, 2013.
Further reading
- Barrell, G. K.; Lapwood, K. R. (1979). "Seasonality of semen production and plasma luteinizing hormone, testosterone and prolactin levels in Romney, Merino and polled dorset rams". Animal Reproduction Science 1 (3): 213. doi:10.1016/0378-4320(79)90003-4.
- Pritchard, D. H.; Napthine, D. V.; Sinclair, A. J. (1980). "Globoid Cell Leucodystrophy in Polled Dorset Sheep". Veterinary Pathology 17 (4): 399–405. doi:10.1177/030098588001700402. PMID 7385575.
- Bowman, J. C.; Hendy, C. R. C. (2010). "A study of retail requirements and genetic parameters of carcass quality in polled dorset horn sheep". Animal Production 14 (2): 189. doi:10.1017/S0003356100010874.