Unusual weather patterns raise nematodirus risk in lambs

Watching weather reports will be critical to managing nematodirus infection during this year’s unusual weather patterns, say experts, as farms report early lamb fatalities.

Independent sheep consultant Lesley Stubbings told Farmers Weekly that cold periods followed by sudden warms spells, which result in a mass hatch of nematodirus parasites, are a “worst case scenario” for lambs six to eight weeks of age.

She advises that the sustainable control of parasites in sheep (Scops) nematodirus forecast should be followed closely, as this is based on weather station data reports and nematodirus eggs start hatching once temperatures reach 10C.

See also: Farmers warned about nematodirus drench resistance

Nematodirus risk factors

  • Grazing – Lambs are grazing pasture that carried lambs last spring
  • Diet – Lambs are eating significant amounts of grass at six weeks and older
  • Groups – Coccidiosis challenge is likely, especially in groups of mixed-age lambs
  • Weather – A sudden cold snap followed by a period of warm weather
  • Stress – Triplets and fostered lambs can suffer higher stress levels

Early in the season the main risk is posed by sunnier south-facing slopes, while later in the season it is north facing slopes that become challenging as they, too, warm up.

“Slowly increasing temperatures lead to a more gradual hatch, allowing lambs to pick up small amounts of nematodirus larvae and develop immunity,” says Ms Stubbings.

She advises farmers to watch the forecast and carry out risk assessments on their various groups of lambs. At highest risk are those grazing pastures that carried ewes and lambs last spring.

She recommends providing “safe pastures” – fields that did not carry lambs last spring – but acknowledges many farms struggle to manage this when grass is tight and sheep are spread thinly.

Benzimadazole (white drench) products are still effective on most farms if the decision is made to treat, adds Ms Stubbings, with faecal eggs counts (FECs) a useful technique to check drench efficacy eight to nine days after treatment.

However, she stresses that FECs cannot be used to decide whether to treat as they don’t detect immature nematodirus.

To see the latest nematodirus forecast can visit the Scops website.