Farm Ireland

Thursday 14 December 2017

The fight to keep bugs at bay

Peadar O Scanaill

At a recent bout of sheep shearing on a lowland flock, the shearer complained about excess mites on his clippers blades.

The farmer was most upset by the shearer's comments as he had been vigilant this year in treating all his sheep.

In fact, the whole scenario resulted in a complaint to the drug company about how ineffective their product was.

The farm vet was called to investigate the affair, as this was a particularly well-run farm that prided itself on the production of premium product.

An injectible version of one of the ivermectin family of medicines had been used to good effect on the farm for several years. There was little or no wool loss and no signs of scratching. That is to say not until the middle of the grazing season.

Samples of wool and skin scrapings were taken and dispatched to the regional veterinary laboratory. But the answer was fairly obvious on initial clinical examinations on the first farm visit.

There are a range of skin parasites that affect sheep in the form of mites and lice. Some of the parasites burrow deeply into the skin and others live fairly much on the surface, eating dead flakes of skin and such like.

In years gone by we used dips to protect against sheep scab; a particularly nasty form of skin parasite on sheep.

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With the advent of injections that can kill sheep scab we have moved away a bit from sheep dips and rely more on other forms of medicine that are easier to administer. And that's where a problem may arise.

The dips were very effective in killing all skin mites and lice. The injections will kill and control almost all of the above group with the exception of the more superficial parasites.

And that's what the shearer found on his blades -- nothing to be concerned about.

One dip later and the flock was clear of the problem.

But it does lead us to why skin parasites are so important in sheep husbandry.

The parasite in the first instance will be living off the goodness it takes out of the host. So immediately, we can see that wastage of food intake is occurring. We are feeding the parasite as well as the sheep.

Secondly, we notice that parasites are more pronounced in animals that are themselves not in good health. When the sheep's immunity is depressed due to any infection, then the skin's natural immunity also takes a hammering.

The parasite then has a field day.

And finally the true cost of skin parasite is borne out by the time and energy the sheep spends scratching the itchy skin.

Wouldn't she be better off grazing to her heart's content, rather than breaking fences with her increscent rubbing.

In some cases the back is so itchy that the ewe rolls onto her back to get a good rub at it.

And we all know what happens then. If not seen and rolled back over again within a few hours, she'll bloat and choke.

And so we're back to the drawing board. Control skin parasites throughout the year using a simple dosing and dipping regime that suits the farm. Consult your farm vet to focus your disease control if in any doubt.

Segregate and treat any new arrivals to the farm before mixing them with the flock. Always remember that a dip may be more effective even though it is much more labourious to carry out.

And don't feel embarrassed if lice or mites turn up in your flock. It makes no difference what school your child attends, the incidence of head lice in children grows alarmingly once the pupils return to the classroom.

We never eradicate these blighters; we simply keep them at bay.

Peadar Ó Scanaill is a Meath-based vet and member of the Food Animal Group of Veterinary Ireland. Email: or call 01-4577976

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