The rise in temperatures in recent days means an increased risk to lambs from hatching nematodirus, according to animal health experts.
Nematodirosis is a particularly nasty disease in lambs, causing a high number of mortalities and stunting the growth of many others.
Under certain climatic conditions it can strike very quickly, with little or no warning. This means sheep farmers have to be on their guard.
The risk has been highlighted within recent days, with the Animal and Plant Health Agency (APHA) reporting two confirmed cases of nematodirosis already – in two different parts of the UK.
Michele Macrelli of APHA said: “We have already confirmed two outbreaks in South West England and the Borders of Scotland, and we expect this to increase in the coming week as temperatures rise.”
Speaking on behalf of the Sustainable Control of Parasites in Sheep (SCOPS), sheep consultant Lesley Stubbings said that nematodirosis could strike very quickly.
"Because the damage is done by large numbers of immature larvae that are not producing eggs, faecal egg counts are not a reliable indicator of risk.
"Rapid action is often required, particularly if you have 2022-born lambs grazing pasture that carried lambs last spring," she explained.
"Lambs typically start eating significant amounts of grass at six to 12 weeks’ of age, although this may be younger if ewes are under stress and not milking well.”
For at-risk lambs, SCOPS advises farmers to movie them to low-risk pasture, which was not grazed by lambs last spring.
Knowing this is not always possible, the alternative is treating with an appropriate anthelmintic. In most cases this is a white (1-BZ) drench.
Individual producers should, however, speak to a vet or adviser and take follow-up steps to ensure the treatment was effective.
Ms Stubbings said: “Roundworms that are resistant to white drenches are widespread within the UK but, fortunately, this is still rare when it comes to nematodirus and these wormers are still highly effective in most cases.
"But remember, it may be necessary to treat lambs more than once depending on the spread of ages in a group and subsequent weather conditions.”
She added: “It is important to assess the risk to each group of lambs based on their age, the history of the field and its aspect and altitude.
"South-facing fields tend to have an earlier hatch and a 100m difference in altitude will change hatching by about +/- seven days.”
