Pasture not vaccine behind orf trouble?
ORF infection in sheep vaccinated against the condition may have more to do with pasture management than any problems with the vaccine, says specialist sheep vet Chris Lewis.
"Sheep grazing among thistles will suffer micro-abrasions, these will allow the orf virus opportunities to enter the animal and infection will set in," says Mr Lewis.
"Spraying thistles early will prevent them being a problem in pastures and reduce the chances of orf infection."
Flockmasters may also misunderstand how the vaccine should be used and this may be causing problems, reports independent vet consultant Tony Andrews. "Orf vaccine is a live vaccine and a level of infection will remain on farm for a period of time after the vaccine is used. It is, therefore, paramount the vaccine is only used where needed, if not it could lead to problems in future years," says Dr Andrews.
Unlike a number of vaccines, the orf vaccine will not transfer any resistance from a ewe to her offspring and it is possible that a very prevalent strain or a high level of infection will overcome any resistance given by the vaccine.
"Flocks with previous or ongoing orf problems should vaccinate at a very young age to ensure immunity is given before the infection has time to take hold." *