Prepare for parasite control in the season ahead, says Merial in new video

Plan ahead for season-long control of parasites to maintain sheep, beef and dairy productivity, is the message in a new Season Ahead video produced by Merial Animal Health.

“All grazing animals are at risk of parasitic disease. The risk may vary between different groups of animals depending on previous immunity from exposure to parasites,” says Merial’s Veterinary Adviser, Sioned Timothy, host of the new video.

“Every farm has its own specific challenge, therefore it’s important to understand regional variations of climate and environment that might increase the risk in a particular area.”

Identifying what parasites are on farm and understanding what the risk period is for each species will help farmers identify at-risk animals, and enable effective parasite control plans to be put in place to protect against losses in production.

There are a number of scenarios facing animals during the post-turnout, early-grazing season.


In beef herds, the main threat to youngstock in the post-turnout period comes from pasture contamination.

Suckler cows, though generally resilient towards clinical disease themselves, will shed low numbers of eggs, which can pose a risk to younger cattle. Depending on the level of exposure to parasites, and the contamination levels of the pasture, a range of management methods, including worming, may be required.

Tom Hume MRCVS, Director at Westover Veterinary Centre, Norwich, and vet for host farm Williams Livestock, discusses the management options available for cattle farmers.

In cattle, the key to maintaining good parasite control is pasture management, ideally maintaining low levels of pasture contamination with eggs and larvae.

Mr Hume says: “Where pasture contamination is low, the dams of spring-born suckler calves will eat most of the existing larvae on the pasture at turnout. The result is that calves will steadily increase their immunity to worms as they graze more heavily in the summer months. This increase in exposure will increase their immunity to gut worms and they are unlikely to need worming until later in the summer.

“However, where pasture contamination is high, calves may need worming earlier in the season. Strategic dosing, combined with monitoring of faecal egg counts will be important to reduce the risk of disease in these animals.”

Autumn-born suckler calves may have received only minimal exposure to parasites in the period before housing and will have very little natural immunity to worms. After turnout, a large number of parasite larvae will be consumed while grazing. These larvae will quickly reproduce within the gut and generate eggs which are passed out onto the pasture ready to re-infect the calves.

“These groups of cattle will benefit from good pasture management, specifically rotational grazing, or strategic worm treatment, in conjunction with faecal egg counts to monitor infection,” says Mr Hume.

Treating with an ivermectin-containing product such as IVOMEC® CLASSIC, or IVOMEC® SUPER, where control of liver fluke is also required, can remove a number of disease-causing worm species, protecting the productivity of beef herds.


Ms Timothy stresses that it’s also important for dairy farmers to remember the impact parasites can have on the current and future production of dairy herds.

She says: “Adult dairy cows may not show outward signs of a worm burden, but gutworms can significantly inhibit their production both in terms of milk yield and fertility parameters1.

“Heifers at grass can be at considerable risk. First season grazing heifers will be completely naïve, having not been previously exposed to parasites. Unless appropriate measures are put in place to control parasitic disease, it can have a severe impact.

“Second season grazing heifers may also be at risk of parasitic disease depending on the level of exposure they received the previous grazing season.” Ms Timothy concludes.

Mr Hume suggests that good pasture management, including rotational grazing, or strategic worming, may be required to prevent disease in these groups of animals.

EPRINEX® (eprinomectin) has a zero milk withhold and is therefore suitable for lactating adult cows, those due to join the milking herd, and youngstock. It removes damaging gutworm, helping to maintain optimum productivity.

All cattle – fluke and lungworm

When it comes to fluke control, the options for treatment vary between beef and dairy animals but the premise for treating is the same. The treatment plan used in the autumn will dictate the need to treat animals for chronic fluke infection (where adult flukes are present) in the spring.

Adult fluke present in animals at turnout will contaminate the pasture with fluke eggs in the early grazing season, increasing the pressure on the pasture in late summer and autumn.

Where this is identified as a risk, Mr Hume advises that it may be necessary to treat cattle for fluke now, to minimize further contamination.

TRODAX®, containing nitroxynil, controls fluke from eight weeks post-infection in beef cattle, and dairy heifers in the first trimester of pregnancy. Controlling fluke can help animals make the most of grass, the cheapest source of feed, and thereby improve live weight gain. The options for treating lactating dairy cows are more limited and product choice should be discussed with a vet or animal health adviser (SQP).

The final cattle parasite to consider is lungworm.

“There is the option to vaccinate, but this needs to be done pre-turnout,” says Mr Hume. “Therefore in most situations strategic worming, in conjunction with advice from your vet, will be the mainstay for lungworm treatment this season.”


“In the period around lambing, ewes may shed increasing numbers of worm eggs, due to a dip in immunity,” says Ms Timothy. “It’s important that this is managed, so that the resulting larvae don’t come to pose a risk to growing lambs later in the season.”

Nematodirus in lambs is normally the main concern post-turnout. Nematodirus may pose a significant risk, especially when lambs are turned out onto pasture grazed by lambs the previous year. Farmers should keep a close watch on the SCOPS or NADIS websites which will indicate when there is a high risk of infection in their region.

Mr Hume says: “Small lambs will often scour from nematodirus infection, with no eggs present in the faeces. This is because it’s the larvae that cause the damage.

“This is a good opportunity to use Group 1 white wormers for nematodirus control, since it is one of the few parasites not resistant to this group of wormers.

“However, care should be taken if lambs are being treated later in the nematodirus season as this may overlap with a potentially wider worm spectrum, which will not be as susceptible to white wormers.”

Pasture management provides a real opportunity to reduce the infection pressure from nematodirus on sheep, and reduce the reliance on wormers.

“If lambs are turned out onto clean grazing (pasture that was not grazed by lambs the previous year) there is virtually no risk from nematodirus infection,” says Mr Hume.

“If however, they are turned out onto paddocks that are used every year, there will be a high risk of nematodirus infection, and lambs will almost certainly need worming in spring.”

Parasitic gastroenteritis (PGE) is the next potential disease to cause illness in growing lambs. PGE has the potential to slow growth, increase finishing times and risk further pasture contamination with worm eggs.

Faecal egg counts (FECs) pooled from susceptible lambs can help identify infection and determine the need to drench. Post-drench FECs, taken at an appropriate time after treatment can also help monitor the efficacy of the product used.

Depending on the individual on-farm risk factors, including any known resistance to specific wormer groups, farmers should employ a range of control measures, including pasture rotation and strategic dosing to effectively manage PGE.

Wormers from Group 3 (clear drenches) such as ORAMEC®, which contains ivermectin, will remove damaging worms and thereby prevent and treat PGE and associated scouring in affected animals. It will also reduce the number of worm eggs passed out to re-infect pasture.

Outwintered and bought-in animals

Outwintered cattle and sheep may require a slightly different approach to parasite control.

“Last autumn was wet and warm and this may have extended the parasite season,” says Ms Timothy.

Animals may have been infected much later than normal, carrying parasite burdens on into the spring. These animals should be monitored to assess the need for worming.

Finally, Ms Timothy reminds farmers to protect their parasite status by considering quarantining bought-in animals, to prevent pasture contamination and the spread of potentially resistant worms. Quarantine is also good practice for other diseases.

Host farm case study – Williams Livestock

Andrew Clarke, owner of Williams Livestock near Norwich, and home to the Williams herd of pedigree British Simmental cattle and the Williams flock of pedigree Blue Texel sheep, talked to Ms Timothy about the parasite challenges they face on farm, and how they deal with them.

The herd was established in 2006 and the sheep flock in 2010, so both enterprises are relatively new. The herd now stands at 35 breeding adults and the flock at around 30 breeding ewes, plus youngstock.

Alongside investing in quality genetics, the Clarkes are keen to maintain a high level of herd and flock health, and work closely with Mr Hume, from Westover Veterinary Centre to ensure they employ the most appropriate parasite control strategy.

Mr Clarke explains: “Careful pasture management and rotation, plus herd monitoring with various health checks throughout the summer, means we tend to treat for all worm species pre-turnout and after housing.

“Over the last couple of years we haven’t had to do any treatments at all while the animals are at pasture. Our calving pattern has been very tight this year, with nearly all the cows calved by the end of March, and we’re seemingly on track with some healthy animals.”

Grazing for the sheep flock is more restricted, which means the Clarkes have to worm more regularly.

“We do rotate the products. At the moment we’re worming the sheep every three to four months. We dose the ewes particularly for fluke pre-tupping, then for worms pre-lambing, and again shortly after turnout and as necessary to keep on top of things.

“We have had problems with fluke in sheep in the past. There was one year with a particularly dry spring time and we became a little bit complacent. We didn’t think it was necessary to worm them that year and it caught us out, and we did have a fluke problem.”

Finally, Mr Clarke advises: “You just have to keep on top of things, and make sure you don’t miss a trick.”

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