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Please note: This article was originally tid-bits from my
column, Michigan Shepherding, in the Black Sheep Newsletter, Number 106. Please contact
BSN for back copies of the originals and stay tuned for more tid-bits in
upcoming issues of BSN. Reprinted in the North American Shetland Sheepbreeders Association News, April 2001, page 6.
There is an article by G. W. Montgomery, written in 1996, about mapping of the horn (HO) locus in sheep. Horn development can range from fully developed large curly horns, firmly attached to the frontal bone, to polled or hornless animals with no horn development, and concave depressions in the skull. Many intermediate types are possible that may or may not be attached to the frontal bone. The presence of horns is controlled by a single autosomal locus (HO) with three alleles:
If the bodies of the horns spiral in opposite directions, they're "conjugate", one being the mirror image of the other, and they should be balanced or symmetrical. Each horn normally has three borders and three surfaces (back, front, and side). These divisions are more difficult to see in a round horn versus the angular type. During growth, many primary or subannual horn rings are formed which resemble wrinkles, ripples, or slight ridges; these are separated by a complementary series of shallow primary or subannual horn grooves. There are deeper secondary or annual horn grooves that occur at approximately yearly intervals due to cessation of growth in winter, periods of drought, or mating activity. Hand-fed rams, removed from their natural environment, and raised under artificial conditions, lack these secondary grooves. |
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