By Dr Clive Dalton
Ageing sheep by their teeth
Sheep have no top teeth. Instead they have a hard dental pad that their bottom incisors bite against. You can estimate the age of sheep by when the front temporary milk teeth are replaced by permanent incisors. They get new ones in pairs working from the middle outwards. But be warned – it can only be an estimate as there is enormous individual variation between animals.
This is what is supposed to happen:
- Lamb - starts with 8 temporary incisor (front) milk teeth
- Hogget - the centre pair of permanent teeth start to erupt at 12 months of age.
- 2-tooth - first central pair of permanent teeth present at 12-18 months old.
- 4-tooth - second pair present at 21-24 months old.
- 6-tooth - third pair present at 30-36 months old.
- Full mouth - complete set of 8 permanent teeth present at 42-48 months old.
Looking in a sheep’s mouth
This is a much simpler job than with cattle but you still need to fully restrain the sheep.
- The easiest way is to sit the sheep upright in the shearing position and use both hands to open its mouth.
Inspecting a sheep's mouth. This picture shows a two-tooth with the next pair have nearly completed their eruption. The lips are being held open by just one hand
- Cup your left hand around its jaw and use your left thumb to lift its top lip and then use your thumb on the other hand to pull the bottom lip down.
- You’ll be able to see if the teeth are meeting the gum correctly and are not “undershot” or “overshot”.
- When undershot the teeth meet the gum back from the edge (called parrot mouth), and when overshot the teeth stick out beyond the gum edge and can be very sharp as they have not been worn down with biting off grass.
- If you want another view, slide your left thumb into the space behind the incisors where there is a gap before the molars start and this will open the mouth so you can see the top of the teeth.
- The sheep won’t like this, so get yourself in a good solid position for when the sheep fights your restraint.
- If you are not able to tip the sheep up, then hold it up against a fence or in the corner of a pen and pull its lips down as described above. You don’t get such a good view.
- You can also do a quick inspection (e.g. secretly in a sale yard) by just sliding you fingers along the front of the teeth to make sure the sheep has teeth, and if they fit the gum. Any that don’t feel normal you can then look at more carefully. You can do a quick udder check with your other hand at the same time!
You can often get a shock when you open a sheep’s mouth and see the state of its teeth. Teeth do an enormous amount of tearing and pulling of fibrous herbage and are subject to great mechanical stresses.
Here are some things regularly seen:
- Overshot and undershot jaws as mentioned above. The overshot teeth may be only partly overshot where the back half contacts the gum and the front half has a lance-like edge that can lacerate your fingers. Sheep with undershot parrot-mouths have great difficulty in eating short pasture.
- Gum cavities that still have both the old tooth present and the new one pushing it out, and the gum looking very inflamed.
- Missing permanent teeth – especially the central pair which are critical for grazing.
- Very long wobbly teeth that are loose in the gum. This may be “periodontal disease” which has many causes and there’s not much you can do about it.
- Most permanent teeth missing and only an odd single very long loose tooth left. It’s better to pull this out to even up the sheep’s bite.
- No permanent teeth at all – the sheep is described as being “broken mouthed” or called a “gummy”. They have all worn off by the gum. In pumice country this can be a special problem with the very abrasive nature of the soil.
- If all the teeth are worn right down to the gum but are still there, it’s very difficult to age the sheep as you cannot tell which stumps are temporary and which are permanent teeth.
- Long permanent teeth where grass has been getting in between them and wearing away great holes.
Sheep with no teeth can still manage to eat if there is plenty of pasture available, as the front teeth only bite off the grass and the back incisors do the grinding. When sheep are fed root crops like turnips, they really need good teeth to break the skin of the bulb and eat it down to ground level once the leafy top has been eaten.
Many breeders have shown that the solution to teeth problems is through an effective selection and culling programme.
This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.