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Nematodirus in springtime lambs

01 May 2020, at 8:15am

As the spring progresses and lambs are out at pasture, we must remain mindful of Nematodirus

Sheep vets will be all too familiar with the phone call from a distressed shepherd that has just found a number of his best lambs dead, which, on post-mortem examination, are found to have succumbed to Nematodirus. So how do we stay ahead of this challenge and advise our clients?

The key is to keep informed and gather as much information as you can. Information of a developing situation with Nematodirus can come from numerous sources. This information can be pieced together like a jigsaw to calculate the risk in your own geographical area. Information may come from NADIS Parasite Forecasts, SCOPS, local post-mortem laboratories, APHA, SRUC and, not forgetting, your own experience both in the current season and previous seasons.

The principle parasite involved in the UK is Nematodirus battus. The parasite has a different life cycle to other sheep worms which is highly dependent on certain climatic conditions (Figure 1). Unlike other roundworms, development of the infective larvae takes place within the egg which allows the larvae to survive from one season to the next and allows transmission from one lamb crop to the next. Hatching is triggered by a period of cold weather, followed by warmer temperatures over 10°C.

If the hatch of Nematodirus occurs over a short period of time, and the lambs are growing well and consuming large quantities of grass, the outcome can be devastating, with deaths and stunted lambs.

FIGURE (1) Nematodirus parasites have a different life-cycle to other sheep worms.
FIGURE (1) Nematodirus parasites have a different life-cycle to other sheep worms.

© Thank you to SCOPS for allowing reproduction of the image

Intake of the larvae will typically lead to scour, which can progress to profuse diarrhoea and wasting. The lambs can become dehydrated and thirsty. The internal damage is caused by migrating larvae. Death can be rapid and prior to any rise in faecal egg count (FEC) so a “wait and see” policy is extremely risky. In my practice we send out warnings to farmers within our newsletters but also through social media, emails and text messages.

If farmers and their vet feel that the lambs are at high risk and the conditions are right, then SCOPS advise using a white (1-BZ) drench which is usually highly effective against this parasite and suitable for young lambs. Care must be taken to ensure correct dosing, good technique and accurate dosing by weighing lambs. Perform a FEC 7 to 10 days later to check that the treatment has been effective but also check for any other intestinal worms which may have survived the treatment.

It is worth noting that other roundworms can also be present in lambs in the early season, which can have very different resistance patterns to Nematodirus. While 1-BZ remains the treatment of choice for Nematodirus, all five groups of anthelmintic are effective. SCOPS produce a very good leaflet detailing many of the different brands which are available (Sustainable Control of Parasites in Sheep, 2020).

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There are five groups of anthelmintics available and there are high levels of anthelmintic resistance to some of these in the UK. In Wales, it is estimated that 94 percent of flocks have resistance to 1-BZ, 68 percent to 2-LV and over 50 percent to 3-ML with reported resistance to 4-AD (Wales Against Antelmintic Resistance Development, 2015). However, note that the flip side of these figures, on 6 percent of farms 1-BZ can still be very effective against all the roundworms.

Every flock should be testing the effectiveness of the different groups of anthelmintic to enable them to use them responsibly and maintain their effectiveness as long as possible. FEC is recommended throughout the grazing season to assess the levels of worms present and also assess the effectiveness of treatments. This can be used alongside growth rate information and any fall in growth rate should be investigated without delay.

The responsible use of wormers has been marketed and talked about for a long while but there is still a slow uptake by shepherds. Vets need to engage with farmers to ensure this and other messages are taken on board and actioned.

The first step to becoming engaged and trusted by your shepherds is to be proactive with warnings and key messages. Consider sending them out to all your sheep keepers in a format that they are going to see and read, and hopefully take heed of. Sheep farmers have traditionally been reluctant to engage with vets and rely much more on advisors and consultants.

If you want your practice and vets to succeed with sheep flocks, we need to make sure vets have the
tools, knowledge and confidence to engage and discuss problems with shepherds. Then, armed with knowledge and confidence, go out and engage with them. In the current exceptional circumstances, this may not be the easiest task, but if vets have time at home or in the car there may be opportunities.

Sit down with the practice management software and make a list of sheep farms. Then make phone calls to some selected shepherds. Once lambing has finished, before the summer season gets into full swing, they may have time to review and discuss. Discussions can take place about the previous lambing, how did it go, were there any major problems or niggles which need addressing? There may be an opportunity to consider ovine abortions and vaccination regimes for the coming autumn. How much antibiotic was purchased from the practice compared with the number of ewes and lambs? There may be an opportunity to improve the health of the flock through reduced reliance on antibiotics or sorting out a problem to reduce the need for antibiotics. The list can be endless.

The late spring time is also a good time to discuss worming protocols for the coming season. Discuss any issues in the previous year, ask how the lambs grew and how quickly they reached slaughter weight. There may be a chance here to discuss and offer faecal egg counting and reduction tests.

These problems occur in many flocks and vets should be at the fore, making ourselves available to help ensure sustainable lamb supply for the future.