12 April 1996

Dont allow roundworm resistance to ruin you

Lambs are at increased risk of picking up worms at grass this year due to the late spring. So an effective worming policy that guards against flock resistance more important than ever. Rebecca Austin reports

SUSSEX flockmaster Richard Froggatt says producers must experience the effect roundworm resistance to white drenches can have on a flock before they realise how devastating that can be.

Resistance is a serious threat says Mr Froggatt, who runs 200 pedigree Suffolks at Stonecross Farm, Wadhurst. Many producers have no idea how perilously close they are to experiencing it, he says. "General complacency is not good enough."

Five years ago the Central Veterinary Laboratory (CVL) took away some dung samples from the farm to be included in one of their worm resistance surveys.     Mr Froggatt was not aware his sheep were harbouring resistance until the CVL came back with the results.

"Thinking back I had made several bad mistakes – but none worse than most producers," he says. "I was certainly guilty of drenching with the same compound too frequently. I was also under calibrating the dose gun and not weighing the lambs. At the time I was buying in a lot of stock which always increases the risk – although they were always dosed either at market or as soon as they arrived home.

"But regardless of what it says on the packet these wormers are not as good as the manufacturers would lead you to believe. What also annoys me is that salesmen are still denying there is a white drench problem even though they are alive to what is going on."

As soon as Mr Froggatt was aware of the problem he took CVLs recommendation and rotated wormers. He used an avermectin for two years and then a levamisole, but then returned to a white drench (benzimidazole).

"That is when I came unstuck," he said. "I had used too much white drench at the exclusion of anything else previously and there was still resistance out there."

As a result he lost two ram lambs in the early autumn. They were part of a group which were set stocked and had just experienced an outbreak of coccidiosis. They were on an ordinary monthly drenching programme using a white drench, but Mr Froggatt says he failed to recognise the worm infection early enough – thinking it was the coccidiosis which caused them to scour.

"Eventually post mortem evidence highlighted the resistance. In the mean time I couldnt afford to wait so gave all the lambs a dose of an avermectin. The transformation was spectacular – within a day or two the lambs had a different attitude to life," says Mr Froggatt.

Further samples

Now he alternates annually between an avermectin and levamisole and is waiting for the CVL to take further samples. He worms the ewes three times a year to try and lessen the worm burden to benefit the lambs. "I dont want the ewes to lay vast quantities of eggs which will infect the lambs," he explains. So they are dosed in the spring when the lambs are first wormed, at the end of the summer before tupping so they can maximise the flushing effect of the grass and at housing eight weeks prior to lambing.

Lambs are generally wormed every month, but that is not a hard and fast rule. "It depends on the weather, what the field had carried the previous year and how I feel the lambs look," explains Mr Froggatt. "Although we are reliant on the chemist in our system, I do want the sheep to have a chance to build up a decent natural immunity. And they dont get that by being full of drugs. Their diet is 100% wormy permanent pasture, but at least they know what life is about and survive when sold onto another farm." &#42

"Mr Froggatt has fallen into the trap of using the same benzimidazole chemical for many years without a break. At the same time he could have underdosed his animals by failing to calibrate the drenching gun or under-estimating animal weights.

"Once benzimidazole-resistant worms are present on a farm they tend to stay. There is little evidence to suggest that benzimidazole-resistant worms revert back to susceptibility, even when other anthelmintic types are used." – Keith Hunt, parasitology department, Central Veterinary Laboratory.


&#8226 Buying-in sheep infected with resistant worms.

&#8226 Underdosing by guessing animal weights.

&#8226 Treating unnecessarily.

&#8226 Changing anthelmintic families more than once a year.

&#8226 Using the same anthelmintic family year after year.

&#8226 Using the same pasture for sheep and goats.

&#8226 Mixing different anthelmintics together yourself.

Source: NOAH

Ewes are dosed before lambing, and again in early May when the March-born lambs are first wormed.

Richard Froggatt stresses general complacency is not good enough.