Polled livestock are livestock without horns, of species that normally have them. The term refers both to breeds or strains which are naturally polled through selective breeding and to naturally horned animals which have been dehorned.[1] Natural polling occurs in cattle, yaks, water buffalo and goats, and in these it affects both sexes equally; however in sheep both sexes may be horned, both polled, or only the females polled.
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Genetics
In cattle, the polled allele is genetically dominant to that for horns. In sheep, the allele for polling in both sexes is dominant to that for being horned in both sexes, and both these are dominant to that for polling in the female only.[2] The development of wholly polled strains in goats is deterred by the fact that in goats the polling gene is linked to hermaphrodism; naturally polled water buffalo also have genital defects.[3]
Scurs
Naturally polled animals occasionally have scurs – small, loose horny growths in the skin where their horns would be. In cattle this trait has been traced to a separate gene (on a different chromosome) from that responsible for polling. However the presence of the allele for scurs can only be seen in a polled animal, because the animal has to be polled to see the scurs.[4] Similar scurs may also occur where dehorning of a naturally horned animal has been incomplete.
Reasons for polling
Polled livestock are preferred by many farmers for a variety of reasons, the foremost being that horns can pose a physical danger to humans, other livestock and equipment. Horns may also interfere with equipment used with livestock (such as a cattle crush), or they may become damaged during handling.
In other circumstances horned animals may be preferred, for example to help the animal defend itself against predators, to allow the attachment of head yokes to draught oxen, to provide a hand-hold on smaller animals such as sheep, or for aesthetic reasons – for example in some breeds the retention of horns is required for showing.
See also
References
- ^ Ekarius, Carol (2008). Storey's Illustrated Breed Guide to Sheep, Goats, Cattle and Pigs. Storey Publishing. p. 319. ISBN 9781603420365.
- ^ Genetics of polling in sheep.
- ^ Caldwell, HS (Editor), 1977. The Water Buffalo. Animal Production and Health Series 4. Food and Agriculture Organization, Rome. (quoted in Charles G. Hickman, Cattle genetic resources, 1991, p 246, Elsevier Health Sciences, ISBN 0444886389)
- ^ Long, C. R. (1978). "Inheritance of the horned, scurred, and polled condition in cattle". Journal of Heredity 69: 395–400.
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