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Monday, 11 May 2015

Dental Diseases
Maintaining healthy and functioning teeth and gums is of critical importance to the body condition/weight gain in adult sheep. Problems associated with incisor tooth loss or disease can lead to malnutrition, as sheep can often not bite off short or rough bits of pasture; poor production and weight loss also follow. Problems associated with molar teeth (eg. Overgrown, worn or absent) often lead to incorrect mastication of fibrous feeds and subsequent weight loss. Mastication is the chewing and grinding up of food; in order to increase the surface area for enzyme efficiency. It is the first step in digestion.

Sheep have 32 permanent teeth. The temporary incisors erupt sequentially at approx. weekly intervals from birth. The temporary premolars erupt within 2 – 6 weeks. The permanent central pair of incisors erupts at 15 months and is in wear by 18 months; the other permanent incisors follow at 6 month intervals. The first permanent molar erupts at 3 and 5 months in the lower and upper jaws. The second permanent molar erupts at 9 – 12 months and the third permanent molar and permanent premolars erupt between 18 – 24 months.
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Incisor teeth alignment: to assess the incisors, they are best examined by running the index finger along the dental pad while the sheep’s mouth is closed. This will show whether there are any teeth projecting forward (overshot jaw or prognathia) or behind (undershot jaw or brachygnathia).

·         Incisor loss (broken mouth): premature loss of incisor teeth is a major problem that leads to early culling because affected sheep are unable to bite short pasture; leading to malnutrition, poor production and weight loss. Traditionally, ewes are culled after about 6 lambs crops due to reproductive reasons; broken mouth may lead to ewes being culled after only two crops, representing major production and financial losses. Broken mouth is readily recognised as the incisor teeth develop elongated appearance, become loose and eventuall are lost. There are no recognised control measures. Management options are few too- sometimes moving broken-mouthed ewes to low ground pastures with higher grass length or higher concentrate of supplementary feed.

·         Dentigerous (odontogentic) cysts: occur very sporadically in young adult sheep. Malocclusion leads to weight loss and poor body condition. The cause of these cysts remains unknown. Typically, sheep aged 2 – 4 are affected, presenting in poor body condition if grazing has been sparse. There is a uniform, non-painful, bony swelling of the mandibular symphysis about 5 – 6 diameter which involves the roots of the incisor teeth. Some of the incisor teeth may have been lost whilst the remaining teeth are often aligned horizontally. Preferential grazing and supplementary feed is advised.


·         Cheek teeth problems: excessive molar and premolar teeth wear, leading to malocclusion and poor mastication of fibrous food, is a major cause of weight loss and poor condition in older sheep. Very sharp enamel ridges develop on the outer aspect of the upper cheek teeth, and the inner aspect of the lower cheek teeth; due to lack of wear on these tooth margins. Cheek tooth loss with consequent unimpaired growth of the opposite tooth into this gap will lead to stepmouth. In general, cheek teeth problems pose more of a significant damaging effect than incisor teeth, due to their grinding function of fibrous feedstuffs. Cheek teeth problems can be best identified by impaction of food in the cheeks and short jerky jaw movements with the mouth held slightly open, as well as fibrous food often protruding from the corners of the mouth when eating, frequently dropping large wads of masticated food from their mouth. Sheep with severe teeth lesions often drop pelleted food when eating and may raise their head while masticating to assist movement of food over the dorsum of the tongue and into the pharynx. Sheep with molar dentition problems are unable to grind feed sufficiently to allow further digestion in the forestomachs. Samples collected at necropsy from the rumen show longer fibre length compared to normal sheep. Bony lesions of the jaw bone (mandible) associated with cheek tooth loss that may suggest root infections are uncommon. There is no treatment and affected sheep should be culled; affected sheep can improve their body score if given generous concentrate feeding over a 10 – 12 week period.


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