Anthelmintic resistance management in sheep – an opportunity for the profession? - Veterinary Practice
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Anthelmintic resistance management in sheep – an opportunity for the profession?

Vetinary Practice learns about SCOPS and the need for a clear strategy on resistance

VETERINARY surgeons have a crucial role in the battle to slow down the spread of anthelmintic resistant (AR) worms, described as the biggest single health threat to British sheep farming at the moment.

“Many farmers do not realise resistance could be in its early stages on their farms, but they need to wake up to the fact that they need to act now,” says Lesley Stubbings, founder member of SCOPS (Sustainable Control of Parasites in Sheep).

“If farmers are going to slow down the progress of AR, they must stop drenching sheep with the same anthelmintic at the same time every year. They need to target their use better and reduce their reliance on anthelmintics where possible and move to quarantine dosing,” she said.

Integrated programme

Supporting her views, Simon Harris, veterinary adviser for Novartis Animal Health, believes that vets can playakey role in implementing integrated worm control programmes to combat AR on farms. He points out that there are only three classes of wormer currently available to farmers in the UK, and resistance is becoming more common to all these classes.

“It is vital we protect these important veterinary tools before it is too late,” he says. “Resistance on any given farm can be detected with Faecal Egg Count Reduction Tests (FECRTs) and its development slowed down, if current SCOPS worming guidelines are followed.

“Unfortunately, the farmer often waits till he sees a reduction in efficacy, which means resistance has gone too far, and little can be done at this stage – and that is where I think vets can step in to help farmers slow down the onset of resistance.

“Resistance management is a developing area of veterinary medicine in which knowledge is increasing all the time,” says Mr Harris.

“As more information is accumulated in this area, we have to consider the next challenge–passing newly accepted resistance management strategies on to farmers via clear messages that can be practically implemented on farm.

“The ultimate is for farmers to follow worming programmes that give good worm control, thus good productivity, while ensuring current and future anthelmintics retain their efficacy. Vets have the knowledge to deliver these messages on farm, using tools such as flock health planning, which can be mutually beneficial to both the vet providing the additional services and the farmer who benefits from improved flock health.

“Vets have a crucial role to play by explaining to sheep farmers that resistance is not a black and white process, but one which is insidious and happens over a period of time – usually years.

“Farmers need to understand that as resistance develops, the proportion of resistant worms increases and the performance of sheep falls, because the number of worms killed when the sheep are treated is always reducing.

“When you realise that sheep farmers could suffer significant production losses in lambs with worms before they can see any clinical signs, you can start adding up the huge cost of AR and understand why they need more assistance from vets,” says Mr Harris.

“For example, vets can help farmers look at alternative ways of controlling the worm burden in their flocks, such as better grazing management. They can also advise farmers on quarantine dosing for all their new stock to avoid bringing new species such as Haemonchus contortus or resistant strains of worms on to farms.

“As we all know, quarantine dosing is a vital process to combat the onset of AR, yet many farmers do not follow the simple guidelines that are provided by SCOPS,” he adds.

The guidelines include:

■ drenching all in-coming sheep with a levamisole (yellow) drench and a group 3 ML drench sequentially to minimise the risk of any resistant worms surviving;

■ then keeping the sheep off pasture for 24-48 hours so all worm eggs have been passed; and

■ finally turning the animals out onto dirty pasture to make sure any eggs from worms that have survived the treatment are diluted by worm eggs already on the pasture

Drench testing

Mr Harris also points out that drench testing after use of any class of wormer to make sure it is effective is a vital tool that vets and farmers can use in the fight against AR.

“Using the right drenching practices, and rotating through all the current available classes of wormer, helps slow the onset of resistance. Getting farmers to use the right product at the right time is vital.

“Through flock health planning of resistance management, vets have an opportunity to get onto sheep farms more often, to give the correct worming advice and develop their farm business – and help them follow best practice, according to the SCOPS principles.”

There are eight basic SCOPS principles:

1. Know the AR status of the farm and the worm species on the farm.

2. Quarantine dose any oncoming animals.

3. Administer your wormers accurately.

4. Don’t over-treat.

5. Select wormers for the species you are trying to treat.

6. Reduce drug dependency – consider other worm control methods.

7. Maintain “in refugia” worms–i.e. don’t expose the whole worm population to a worm drench.

8. Have a farm specific control strategy devised by a veterinarian or adviser.

lThe SCOPS Technical manual for veterinary surgeons and advisers, providing the latest advice on the control of parasites in sheep, is available on the National Sheep Association (NSA) website… /pdf/scopstechmanthree.pdf.

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