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The age of cattle is determined chiefly by examination of the teeth, and less perfectly by the horn rings or the length of the tail brush; however due to bang-tailing, which is the act of cutting the long hairs at the tip of the tail short to identify the animal after management practices, the latter is least reliable. ==Teeth method== Cattle are placed in a cattle crush in order to restrain them prior inspecting the mouth and amount of teeth that each animal has. The temporary teeth are in part erupted at birth, and all the incisors are erupted in twenty days; the first, second and third pairs of temporary molars are erupted in thirty days; the teeth have grown large enough to touch each other by the sixth month. Temporary incisors or "milk" teeth are smaller than the permanent incisors. Cattle have thirty-two teeth, including six incisors or biting teeth and two canines in the front on the bottom jaw. The canine teeth are not pointed but look like incisors. The incisor teeth meet with the thick hard dental pad of the upper jaw. Cattle have six premolars and six molars on both top and bottom jaws for a total of twenty-four molars. The teeth of cattle are designed primarily for grinding, and they use their rough tongues to grasp grass and then nip it off between their incisors and the dental pad.〔(Nutrition and Feeding of the Cow ) Retrieved on 26-3-2009〕 There is controversy on the reliability of attempting to tell the age of cattle by their teeth, as rate of wear can be affected by the forage that is grazed. Drought or grazing on sandy country will also affect rate of wear. The following is a guide: * 12 months - All the calf teeth are in place. * 15 months - Centre permanent incisors appear. * 18 months - Centre permanent incisors showing some wear. * 24 months - First intermediates up. * 30 months – Six broad incisors up. * 36 months – Six broad incisors showing wear. * 39 months – Corner teeth up * 42 months – Eight broad incisors showing wear. The development is quite complete at from five to six years. At that time the border of the incisors has been worn away a little below the level of the grinders. At six years, the first grinders are beginning to wear, and are on a level with the incisors. At eight years, the wear of the first grinders is very apparent. At ten or eleven years, used surfaces of the teeth begin to bear a square mark surrounded by a white line, and this is pronounced on all the teeth by the twelfth year; between the twelfth and the fourteenth year this mark takes a round form.〔The Household Cyclopedia of General Information, 1881〕 It is a requirement in some locations that prime cattle have a dentition indication mark on them prior to auction. This is normally done by the vendor, or the stock agent. Fat cattle auctions in New South Wales, Australia identify the amount of teeth that prime animals have in the form of sprayed marks along the back. Thus two tooth cattle are marked on the wither, four tooth on the middle of the back and six tooth on their high bone (near tail). Milk and eight tooth cattle are not marked. 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「Cattle age determination」の詳細全文を読む スポンサード リンク
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