Shepherds are being urged to remain vigilant for signs of orf in growing lambs this grazing season, particularly if pastures are prone to thistles, and animals have not yet been vaccinated.
Orf is caused by a virus that only grows in the surface layers of the skin, but the virus will only cause an infection if the skin is already damaged.
If the disease does break out at grass, infected lambs are less likely to finish on time, MSD Animal Health technical manager John Atkinson warns.
A recent study found lambs affected by orf were 10% lighter than disease-free animals after an outbreak.
Orf infections in any young sucking lambs can quickly spread to ewes, causing sore teats and mastitis, which can be very serious, even fatal.
- scabby lesions around the mouth and nostrils
- the infection may also affect other parts of the body, including the inside of the mouth, the lower legs and, in particular, the teats of nursing ewes.
While the virus can strike at anytime of the year it is most commonly after lambing while sheep are at grass.
“Orf is a continuous threat and is quite often seen in older lambs that have picked up skin abrasions while grazing,” says Dr Atkinson.
“Orf is caused by a virus, and before it can cause disease it needs to get into the surface of the skin.
“This usually happens through cuts and scratches, no matter how small.
“One of the most common causes for these are thistles, which can easily break the skin around the mouth as the lamb grazes, and if the orf virus happens to be present on the skin, it can then easily infect the animal and cause disease.
“It is not only thistles that you need to pay attention to; nettles, brambles, rough grazing or cut foliage from hedge trimming could also lead to skin damage and subsequent orf outbreaks.”