Parasite Watch, Sheep farming


Warm, wet weather is causing a sudden rise in worm egg counts and could pave the way to an earlier fluke season this year, according to the latest results.

Results from farms involved in the Zoetis Parasite Watch scheme shows that areas which have seen warm and dry weather followed by sudden wet weather, such as South West Scotland and Wales have seen a rise in worm egg counts.

Egg counts across the country have shown that Nematodirus counts have been later this year than in 2016 and have been part of mixed counts with other worms, this affects the advice that SQPs and vets have been giving regarding treatment choice, as products must be effective against all the worms present.

At Graeme Mathers’ farm, Fern, Angus, during June the faecal egg counts were 315 eggs per gram (epg) and Nematodirus up to 420 epg.

When analysing results, 250 epg is a suggested cut off for most worms, above this it is high enough to be causing production losses.

In Peeblesshire at Posso Farm, a testing in June revealed Nematodirus up at 735 epg and worm egg counts at 350 epg. Normally Nematodirus counts would be expected earlier. These results have very beneficial as the mixed burden changed the treatment choice.

It is very likely that the weather has played a part in the late Nematodirus challenge. The end of May and beginning of June was really dry and warm, but towards the middle to end of June it got wetter, providing perfect conditions for the eggs to hatch. Dry weather followed by sudden rain and an increase in temperatures is the perfect climate for worms, which is why we are seeing some higher counts

Although Nematodirus is being picked up in many samples, it may be less of a risk now than it would have been earlier in the season as immunity develops quite quickly in comparison to other worm species, so if they have been previously exposed, they may have some degree of protection.

Post-drench tests

In order to check you have selected the correct wormer, it is a good idea to take a post-drench test.

A post drench test is a crude, simple test, but can give an indication of any resistance or under dosing issues in the flock. It won’t give a percentage resistance figure but can show that resistant worms are present. Post drench testing requires a faecal egg test being taken either one (yellow group) or two weeks post treatment from any lambs.

If there is an egg count after testing then it could either be under-dosing or a potential resistance issue. However, the result can also get a false negative, as the lambs being tested post treatment may not have had worms to start with, so there would have been no worms to kill, hence the negative result

So far, Parasite Watch has helped our farms identify potential issues and go onto to do a faecal egg reduction test to find out how bad the resistance issue is.

Resistance is classed as any product that is not killing at least 95% of the worms. Above this level, production losses will be minimal. However, below this effectiveness production loss will be occurring, resistance needs to be at around 50% before continued clinical disease will be notable.

So, investing in post treatment tests can pay off if it means you are not using a product that isn’t fully effective.

A new and free online tool can help SQPs demonstrate to sheep farmers the cost of using the wrong wormer on their farm.

The App

The Sheep Drench Cost Calculator from Zoetis will help farmers, in conjunction with their advisors, decide which wormers to use on their farm. The app demonstrates the potential loss in growth rate, labour and medicine cost, when the wrong product is used. The calculator uses the latest UK resistance data or bespoke farm data so farmers can create specific drench plans with costs and return on investment information.

Although some wormers may be more expensive, the effectiveness against worms is likely to be higher because there is reduced resistance.


The change in the weather could also spark the start of an earlier fluke season, now is the time to discuss your plans with your advisor to get on top of the problem early to reduce the threat to animal health and to reduce pasture contamination.

Treating for fluke isn’t something we normally think about until nearer to tupping time. however, there is the potential to get caught out It takes 12 weeks from a sheep becoming infected with fluke to producing egg laying adults, which will go on to contaminate the pasture for next year. There is a test that can pick up immature fluke at around six weeks of age. If you can test and treat earlier you are stopping the lifecycle before they produce these egg laying adults. This is not only better for the animal, but will also reduce pasture contamination for later and next year.

Over the next month, farms involved in the Zoetis Parasite Watch scheme will be testing for fluke. We will bring you the results in next month’s article.

For further information please contact Zoetis UK Limited, Walton Oaks, Dorking Road, Tadworth, Surrey KT20 7NS. Customer Support: 0845 300 8034.

Use medicines responsibly ( Date of preparation: July 2017 AH558/17