A mild March saw much of the UK experience above average temperatures and mixed rainfall. The NADIS parasite forecast recommends sheep farmers plan and target their parasite control for the coming months.
In sheep, severe outbreaks of nematodirosis can often occur in May. A cold late-spring followed by a sudden rise in temperature can trigger a synchronised, mass hatch of infective larvae on heavily contaminated pastures grazed by last year’s lamb crop.
If susceptible 6-12 week old lambs are grazing then scouring, serve production losses and sudden deaths may follow. As a result of the mild average temperatures in March the NADIS and SCOPS (Sustainable Control of Parasites in Sheep) Nematodirus forecast predicts an early spring hatch. This will spread from south to north, posing a moderate to high risk to early lambing flocks with susceptible grazing lambs.
Wormer treatments should be administered to at risk lambs to prevent disease. Where outbreaks of clinical disease do occur it is important to treat all lambs in the group immediately.
White drench (1-BZ) wormers are still recommended to control nematodirosis, although the risk of resistance to this group should be borne in mind: low levels of resistance have been detected in Nematodirus, but resistance is widespread in the other major worm species.
Ten days after treatment, the faecal egg count (FEC) of a pooled faecal sample from the group should be checked for evidence of a persistent Nematodirus burden or eggs of another worm species. If eggs are present, further investigation and retreatment may be warranted if samples suggest persistent infection. Visit www.nadis.org.uk or SCOPS www.scops.org.uk websites to monitor Nematodirus activity in your region.
The risk to sheep of parasitic gastroenteritis increases as mid-summer approaches. Ewes previously treated with a short-acting wormer at turnout, grazing heavily infected pastures, may require further worming treatment. Aim to leave about 10 per cent of the ewes untreated, targeting those in poor body condition or with a high FEC.
Lambs on contaminated pastures may need to be wormed from six weeks of age onwards, taking into account the Nemarodirus risk. Lambs on safe grazing should not need worming until weaning.
High rainfall in May and June can lead to an increased risk of fluke in sheep later in the year. On farms with a known fluke problem wet conditions will favour proliferation of the snail intermediate hosts and, promote infection by miracidia released from fluke eggs shed earlier in the spring.
Merial’s veterinary advisor Sioned Timothy says: “Sheep should be treated in the spring to remove egg laying adult fluke and to limit pasture contamination with fluke eggs early in the season. We suggest using a product that targets the later stages of the parasite such as one containing nitroxynil, which is effective against late immature and adult fluke. Using an alternative active to triclabendazole at this time of year, when immature fluke are not the target of treatment, will help to reduce selection for resistant strains of liver fluke.”