Map helps forecast next nematodirus outbreak

A new forecast is helping sheep producers accurately predict the timing of the next nematodirus outbreak, writes Nerys Wright.

Significant variations in weather conditions make forecasts difficult from year to year. But when an outbreak does occurs, it can rapidly cause severe harm or even death in a large number of lambs.

Treating too early or too late can result in huge production losses. However, there are some factors that we can use to determine when our risk is higher and when treatment would be beneficial.

These factors are:

• The age of the lambs: Nematodirus tends to affect young lambs 6-12 weeks of age. They are old enough to be grazing and ingesting larvae from the pasture but have not yet acquired immunity.

• The temperature: Eggs present on the pasture typically require a period of cold weather followed by warmer temperatures of 10°C or more to hatch. If these conditions occur in quick succession, a large number of eggs can hatch at the same time, triggering a mass hatch whereby the intake of ingested larvae through grazing is huge and causes damage quickly.

This is where the SCOPS Nematodirus forecast map proves useful. The interactive map, updated daily with data from 140 weather stations, provides a guide to the risk level in your area.

To assess the risk for each group of your lambs, consider the field’s history, aspect, and altitude. South-facing fields typically experience earlier hatching, and for every 100 meters increase in altitude, hatching is delayed by about seven days.

For example, if your nearest weather station is at 200 meters above sea level and your farm is at 100 meters, hatching could occur around seven days earlier than the forecast on your farm.

Faecal egg counts (FECs), while they are a great tool for other parasites, are not reliable indicators of current risk for Nematodirus because the damage is caused by immature larvae.

Larvae will not be present in faecal samples. Waiting for adult eggs to appear is not advised. The map is available on the SCOPS website at www.scops.org.uk.

Nerys Wright is an independent sheep consultant. For more details, call 07891 187643 or visit sheepconsultancy.co.uk.