VET’S DIARY: Itchy sheep can be a sign of lice or scab infestation

Slowly the cycle of work is changing again from cattle pregnancy scaning and Johnes/TB testing to sheep scanning result discussions and itchy sheep investigations.

While itchy sheep can be seen at any time of year, we tend to see an increase in occurrence during the winter. A combination of favourable mite conditions and longer fleeced animals makes this season ideal for ectoparasite problems.

Often the cause of this is down to one of two creepy crawlies – namely lice and scab. I have already diagnosed lice infestation in three flocks in the last two weeks.

However we have also diagnosed scab on three different unconnected farms in the last month.

The signs of both scab and lice can look remarkably similar, however the treatment is not. It is important to be sure of the cause of the itching and wool loss before treating the flock, otherwise you risk wasting both time and money on the wrong treatment.

Heavy lice infestations are often possible to diagnose with the naked eye. Lice can be seen walking across the fleece. However, it is possible to have scab and lice on the sheep at the same time therefore more investigative work is needed. This takes the form of skin scrapes and fleece samples which we look at under the microscope to identify the offending insect.

If scab is identified it is best practice to inform your neighbours. This is not a good job but there should be no stigma to having scab, more of a concern is not being open about it and working together with sheep neighbours, as generally if it is diagnosed on one farm then neighbours, while not showing signs, will already be infected. Normally we will then holding a meeting in a nearby village hall with all the neighbouring sheep farms and everybody can agree a co-ordinated treatment time for every single sheep in the district. This way it can be cleared out. Otherwise it just circulates round from farm to farm and causes ongoing production losses and treatment costs.

Worryingly, we are already finding resistance to the sheep gut worms which are also killed by the scab treatment injections so they should not be overused.

Once the cause is identified, it is important that as well as using the correct product, the treatment is given in the correct way. Under dosing of animals, or missing the odd sheep is easily done and will result in failure to eliminate the problem.

For lice it is important the right nozzle is used as merely spraying the product onto the wool will not control the lice which live near the skin.

Sheep straying onto your fields, bought-in animals, shared handling facilities or wool tags being transferred from a boilersuit to your farm are all potential methods of bringing an ectoparasite problem onto the farm.

Scab is able to live off the sheep for 17 days. Effective quarantine treatments and isolation should stop it being brought onto the farm which is the commonest means of spread.

In addition to lice and scab, there are various other causes of skin disease in sheep, including other less common mites, eg chorioptes can cause problems, particularly to tup heads, scrotum and back of hocks/feet. Often these scrotal mange mites are only picked up at pre-tupping testing but some cypermethrin applied to the scrotum now in tup hoggs helps prevent the problem.

Some bacterial infections can also cause significant wool changes and itching such as lumpy wool.