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Livestock
Spring turnout: Your guide to worming responsibly
be improved upon. Co-grazing mixed ages is another strategy. “Beef calves are always co-grazed with their mums, whereas dairy calves – which are typically higher stocked and more intensively grazed – don’t have mum going around hoovering up all the extra larvae,” Mr Palmer explains. “And the mum represents an in refugia population of worms that are not exposed to the drugs as well because she doesn’t get treated. This helps maintain the worm's susceptibility to anthelmintics. “Co-grazing in a rotational system with older cattle or sheep, especially with calves at the head of that rotation so they’re constantly going onto clean new grass. The difficulty is when you run out of that and start to bring them back round again. They’re then back on same pasture three weeks later and the worms have had a nice easy time maturing, so that’s where rotational grazing lets you down a bit.”
What actives are available and when should they be used?
As we prepare to turn calves out to pasture, livestock editor Sarah Kidby spoke to Norbrook veterinary advisor Douglas Palmer for advice on available worming strategies, and how to reduce the risk of resistance. As AHDB Dairy suggests that dairy heifers take an extra three months to reach breeding weight when burdened with gastrointestinal parasites, at an extra cost of £260/head, managing this risk ahead of turnout is a priority. In order to calve down at 24 months, dairy calves need to meet growth rates of 700g/day to bull at 15 months. Anything that slows this process down will naturally increase costs and reduce overall lifetime productivity. Although resistance is well recognised in the sheep industry, it is less widely reported in the cattle sector – however, lack of data means it could be a bigger problem than we realise, and it’s important not to be complacent. “Probably the most economically significant worm species would be Ostertagia ostertagi in cattle, but where resistance has been found, it has been identified more with Cooperia species, which may be less pathogenic,” Mr Palmer explains. “We need to be using our medicines more sustainably – not relying on anthelmintics but incorporating other strategies to control worms. Ostertagia resistance has been seen in other parts of the world so we do need to be careful.”
Diagnostic testing One thing Mr Palmer believes could be utilised more on farm is monitoring weight gain for targeted selective treatment. He recommends weighing every 4–6 weeks to check the growth rate is being met and if not – assuming there is no other obvious cause – consider whether that individual needs worming, as parasite burden is one of the more significant causes of poor weight gain.
Alternatively, monitoring pooled faecal egg counts (FECs) every 3–4 weeks in young calves can be used to identify groups of calves carrying heavier gut worm burdens. The difficulty with both options is fitting these in with lungworm – which needs relatively fewer worms to cause disease but can mature on pasture within a week, so farmers can get caught out when doing selective treatment and faecal egg counts. “The way to help avoid this is to vaccinate for lungworm,” Mr Palmer notes. Vaccinating calves for lungworm should be completed before turnout, then targeted selective therapy or FECs can be started around 3–4 weeks later. If these are clear, repeat in another 3–4 weeks and treat if worm burdens are rising.
How to reduce the risk of resistance Ensuring drugs are used correctly and applied in the right way is important. “The advice within the industry is always to dose groups of animals based on the heaviest in the group which I always say is great advice as long as the heaviest in the group isn’t twice the weight of the lightest. If you overdose a drug there’s a chance of a toxic reaction, and overall you use more anthelmintic, adding to the cost,” Mr Palmer explains. “Pour ons should be applied to cattle midline down the back on the flattest part of the back between the withers and the tail head. In order to do that properly, the animal will probably need to be restrained.” Checking that wormers have been effective with follow up FECs is another area that could
The three groups are – group one: benzimidazoles (white); group two: levamisole (yellow); and group three: macrocyclic lactones (ML – clear), for example ivermectin, doramectin etc. Drenches are perfectly good options but more difficult to administer and have no persistence, Mr Palmer explains. The benefit is reduced risk of inducing resistance, but when you’ve got a worm problem you might find you have to administer it every month. Whereas ML products have some persistency – some ivermectin pour ons have a two-week persistency for Ostertagia ostertagi. For ivermectin products, Mr Palmer says: “While traditionally calves would have been drenched at three, eight and 13 weeks, it is now reasonable to turn out, do FECs and if the levels start to go up, give the first dose, then check again 4–5 weeks later – keeping a close eye on lungworm, having hopefully vaccinated beforehand.” Doramectin is the active substance in Norbrook's Taurador product, and it has a five-week persistency for Ostertagia ostertagi. “Traditionally it was administered with an eightweek treatment interval, but we’ve tried to move away from that [...]. The more responsible thing to do is turnout, wait three weeks, do a FEC and look at treatment from there.” Mr Palmer adds: “Then there is the moxidectin, particularly the injection which was really aimed as a one-off shot. And the benzimidazole pulse release bolus, which is a pulse therapy so the calf gets a pulse every three weeks, with a gap in between where the calves get a bit of exposure to the worms. As a benzimidazole, there’s no evidence of resistance in the UK as yet, but the downside is this is relatively more expensive. “By late summertime, if you’ve had to use quite a lot of say macrocyclic lactones, it would seem reasonable to think about trying to put in a different active ingredient at that point, like a levamisole or a white wormer to try and reset any early resistance developing,” he continues. For more worming advice ahead of turnout, speak to your vet or RAMA. For details on Norbrook farmer meetings on responsible use of medicines, contact Norbrook or your local vet. FG
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