A mild march saw much of the UK experience above average temperatures and mixed rainfall, which has lead to an increased spring parasite risk for sheep.
The NADIS parasite forecast, sponsored by Merial, recommends sheep farmers plan and target their parasite control for the coming months.
In sheep, severe outbreaks of nematodirosis can often to occur in May, and a cold late-spring followed by a sudden rise in temperature can trigger a synchronised mass hatch of infective larvae.
If susceptible, six to 12-week-old lambs that are grazing then scouring could result in severe production losses, and sudden deaths may follow.
As a result of the mild average temperatures in March the NADIS and SCOPS nematodirosis 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 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 nematodirosis , but resistance is widespread in the other major worm species.
Ten days after treatment, the faecal egg count of a pooled faecal sample from the group should be checked for evidence of a persistent nematodirosis burden or eggs of another worm species.
If eggs are present, further investigation and re-treatment may be warranted if samples suggest persistent infection.
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 nematodirus risk.
Lambs on safe grazing shouldn’t 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.
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For more information please visit nadis.org.uk or scops.org.uk.