Anthelmintic resistance continues to hamper UK farmers

Anthelmintic resistance is becoming a widespread problem across the UK – so what can farmers do to get the best value out of worming products? Olivia Cooper reports.

British farmers spend more than £80m a year on wormers, but a large number are over-dosing or using products that are no longer fully effective on their farms.

According to EBLEX, producers could slash the number of doses administered each year by 35%, yielding an average saving of £663 a farm on wormer costs alone. This reduced reliance should also help delay or eliminate wormer resistance – something which is becoming a serious problem in many parts of the UK.

“Drug resistance is the big growing problem with worm control,” says Dr Gerald Coles, visiting research scientist at Bristol University’s veterinary school. “I would be very surprised if there are any farms in the South West that don’t have some anthelmintic resistant worms – and it will affect their livelihood.”

Internal parasites are a drain on the entire industry, says Richard Phelps, director of Blade Farming and Southern Counties Fresh Foods. “From an abattoir point of view, the biggest problem we have is offal waste – 50% of livers in cattle are damaged in some way, so it is a huge issue. And it’s a very similar story with sheep; a huge amount of livers and kidneys are wasted.”

In fact many abattoirs have invested in better technology to track damaged offal back to the farm of origin, to pass the information back down the chain to producers.

In 2011, 22% of cattle livers and 6% of sheep livers were rejected due to fluke, with a further 8% of sheep livers rejected due to Cystercircus tenuicollis (bladder worm), says Dr Phil Hadley, senior regional manager at EBLEX. This is estimated to have cost the processing industry nearly £4m, but it doesn’t reflect the losses at farm level.

“The losses associated with fluke infection can be significant – £25-30 for every infected beast – due to slower weight gain and lower feed conversion. In sheep it is estimated to reduce weight gain in ewes by 10% and 30% in lambs, which could cost up to £26,000 a year in lost productivity in a 500-ewe flock,” says Dr Hadley.

Tackling worms without resistance

The first thing farmers can do to tackle worms without increasing the risk of anthelmintic resistance, is to only treat animals when they need it, says Dr Coles. “Get a faecal egg counting kit – quite a lot of farmers are using FECPAK which costs about £800 +VAT, which will pay for itself in the first year by reducing unnecessary dosing.” Alternatively, they can take faecal samples to be tested by their vet.

Typically, producers should treat cattle when worm egg counts reach 300 eggs/g, or 300-500 eggs/g for sheep – although that does vary according to age of stock and weather conditions. “A lot of people like to treat ewes at tupping, but unless they are in poor condition it is not usually necessary,” says Dr Coles.

Healthy animals with strong immunity will cope better with worms than those that are under stress, he adds. “The immune system needs a lot of protein to fight worms – and pregnant ewes need that protein to grow the lamb or make milk.”

This often leads to a rise in worm egg shedding around lambing time, contaminating pasture for the growing lambs, so it is worth treating ewes just prior to lambing.

What’s more as animals grow older, they often develop a level of resistance to worms, and it is important to maximise that, adds Dr Coles. “Most spring-born suckler calves will not need treating before they are housed, whereas autumn-born calves will have grazed for longer so are more likely to need worming.”

And by exposing calves to a reasonable level of worms – but not so great as to challenge their health – farmers will produce strong adult cattle that hardly ever need to be treated. “You can measure their immunity at housing using a blood pepsinogen analysis, which will tell whether the exposure has been at the right level,” adds Dr Coles.

He says adult sheep will also develop some resistance, with some breeds proving more resilient than others. “Resilient sheep will still shed worm eggs, but without displaying any symptoms. So don’t breed from ‘wormy’ animals.”

Instead of treating the entire flock, producers should select those that actually need to be wormed. “The majority of worms are in the minority of animals, so look for those that have a dirty back end, a dull coat, or poor appetite, and leave the rest,” he adds.

Dosage

A huge number of farmers under-dose, reducing the efficacy of the treatment, and increasing the risk of anthelmintic resistant worms. It is therefore essential to get the dosage correct, says Dr Colges. “Check your dosing gun is delivering the right amount, weigh your stock, and treat to the heaviest of a group.”

However, even if farmers get all of this right, some drugs may not work. And in a recent informal trial, 73% of farms in the South West found Benzimidazole was less than 50% effective. A third of farms found Levamisole was less than 50% effective, with a quarter finding Ivermectin less than 50% effective. “Efficacy should be 95% or higher – once you get down to 80% you will get real problems,” says Dr Coles.

The most common symptoms of a worm burden are scouring, poor weight gain, lack of appetite and loss of condition – although this varies according to the type of parasite concerned. Lungworm causes coughing and can lead to secondary infections like pneumonia, while blood sucking parasites like Haemonchus contortus result in anaemia.

Dr Coles says: “A Haemonchus female can lay 5,000 eggs in a day – in four days it can theoretically produce enough infection to kill a lamb.”

In sheep, liver fluke can cause anaemia, weight loss, reduced liver function and Bottle Jaw, although acute infection results in a swollen abdomen and rapid death. Cattle get an enlarged bile duct – and identification using faecal egg counts can be difficult as the eggs are not excreted consistently.

“The best form of diagnosis is using an ELISA test on blood, milk or faeces, which can be repeated 14 days after treatment to check it has worked,” says Dr Coles.

The best treatment for fluke is Triclabendazole, as it kills both adult and juvenile parasites – but there is now resistance to this drug in Wales, Scotland and Ireland, so producers may have to resort to single-stage wormers, he adds.

Ascertaining resistance

To discover whether the worms present on a farm are resistant to certain anthelmintics, producers should carry out a faecal egg count before treatment and 14 days later – ideally from the same 10 animals.

Dr Coles says: “More than 80% of sheep farms in the South West are likely to have white drench resistance – and a lot have resistance to all three major anthelmintic groups. In addition, probably 70% of beef farms have resistance to macrocyclic lactones like Ivermectin.” Treating with those products will therefore be ineffective, and a waste of money.

Fortunately sheep producers can use a new product – Montepantel – where they have broad resistance to other anthelmintics. But unless used properly, it is only a matter of time before new resistant strains develop.

To protect against that risk, and to reduce resistance to other products, it is essential that farmers follow one golden rule. “For years farmers were told to worm and move, but that’s the worst thing you can do, because the only worms that survive on the clean pasture are the resistant ones,” says Dr Coles.

In one trial, he changed a completely susceptible worm into a 100% resistant strain in just three generations by selecting the most resistant parent stock – this is what happens when farmers worm and move stock to clean pasture. Instead, they should worm and turn onto contaminated pasture, to dilute any resistant strains with those that are still susceptible to anthelmintics.

When bringing new stock – even a single ram – onto the farm, producers should treat it with Moxidectin and Montepantel to wipe out any worm burden, and quarantine the animal on concrete for 24-48 hours before turning it onto contaminated pasture.

“Just one animal can introduce resistance across the whole farm. There is no easy answer, but no-one wants to be wasting money using drugs that don’t work,” adds Dr Coles.

Case study: Group collaboration

A group of Dartmoor farmers are joining forces to tackle anthelmintic resistance as part of the Healthy Livestock Initiative, organised by Duchy College.

“We are all putting our sheep onto the common, so can’t do anything about the land,” says Layland Branfield, who keeps 600 ewes at Moorlands Farm, Princetown, Devon.

The 10 farmers plan to buy at least one faecal egg counting pack, which will enable them to better target wormer use, as well as discover the resistance status of parasites on their land. In addition, they plan to examine tick-borne diseases, fertility and mineral deficiencies.

“We have cobalt, selenium, iodine and copper deficiency on the moor, which lowers the sheep’s natural immunity, and impacts directly on fertility, health and worm burdens. If we can get the underlying basics right, we can then start to tackle the consequences,” says Mr Branfield.

He doses lambs once a year when clipped in July, before he sells them in August and September. Ewes are treated for worms and fluke in October before tupping, again for fluke in the New Year, and have another dual dose before lambing in March.

“We have 250 acres of improved grass, which is more intensively grazed and difficult to manage than the moorland. We want to buy the kit before April, so we can get it up and running this season, and roll it out to help more farmers in the area,” he adds.

Case study: Cost savings achieved

Clive Rowland has been reaping the benefits of faecal egg counting at Home Farm, Garrowby, Yorkshire, for five years, having taken part in the PARASOL project in conjunction with Innovis from 2007-09.

Initially using the FECPAK kit for his 700 commercial ewes and lambs, he then rolled it out across 120 suckler cows and calves. “It’s been a real eye-opener – we had been routinely worming, and having tested the animals we realised we were spending money completely unnecessarily,” he says.

The project revealed some resistance to white drench, and a suspected start to Ivermectin resistance, so Mr Rowland now rotates wormer types each year to try and slow further resistance building up.

He treats all bought-in shearlings with a yellow drench and Dectomax, and isolates them in the handling pen or a dedicated paddock for at least two days before turning them out onto the main farm. Although the suckler herd is closed, he tests any new stock bulls before turnout. “You need to be sure of what you’re bringing in,” he says.

Mr Rowland tests the ewes before tupping – and has not had to treat them once. He then worms them at lambing time before turnout, and checks faecal egg counts throughout the summer. “It’s fairly simple – it takes about 10 minutes to collect some fresh muck as you’re checking the stock, and 15 minutes to test it.”

Before taking part in the project, he routinely gave a bolus to the maiden heifers before turnout in the spring. “We realised they had no real chance to build up any immunity. We’ve stopped the bolus and have not seen any negative consequences. At nearly £5 a head across 50-60 heifers that’s a significant saving,” he adds.

Suckling calves are no longer wormed – although they are treated at weaning – resulting in a saving of about £200 a year. And by rotating sheep and cattle grazing with silage leys, Mr Rowland keeps a lot of his pasture relatively clean, and now just monitors the rest of it, treating stock when needed.

“It’s made us realise that some animals never need worming, and others might look a bit dull when it is not a worm problem – there is something else that might be wrong,” he says.

Having slashed sheep wormer use by 57% – a saving of nearly £500 – and cattle wormers in half, he is convinced of the benefits. “This year our ewes have scanned at the highest we’ve ever had. I will certainly continue to use FECPAK – it has more than paid for itself.”

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