Dipped all sheep on farm last september.Have a bunch of tup lambs that started scratching mid december so took a couple to the vet and they confirmed it was scab.They were weighed and treated accordingly with Cydectin 2%.Stopped scratching buy after a month started again so took 2 to the vey but vet couldnt see any scab or lice even though they took 3samples from each tup.Their in a shed with no contact with other sheep buy keep rubbing against the wall and trough etc.No visible sign of redness or scabs or sores but lost the odd patch of wool.Could it be anything else?Thanks