Parasite Watch, Sheep farming

Watch out for Nematodirosis

Parasitic gastro-enteritis (PGE) (worm scours) will affect all lambs to a greater or lesser degree and as such are a key concern for sheep farmers everywhere. It can be caused by many different worm species, but the two most important in the UK are Teladorsagia circumcincta and Nematodirus battus.

Teladorsagia tends to build up on pasture through the season after being shed by older animals the parasite has overwintered within, especially ewes around lambing time, the so called “Spring Rise”. Nematodirus can cause explosive outbreaks of disease and even death amongst young grazing lambs. Ewes are immune to Nematodirus worms and do not carry significant numbers of adult worms and therefore do not contaminate pasture. In lambs the worms affect the surface of the small intestine where they damage the intestinal wall as they feed from the digesta. The parasites are relatively large and usually numerous. As few as 2,000 parasites can cause severe inflammation of the intestine, with acute onset scour, lethargy, abdominal pain, rapid weight loss, dehydration and death.

Nematodirus battus

Image 1 – Nematodirus battus from the intestine of a lamb

This condition typically affects young lambs between six and twelve weeks of age. This happens when large numbers of eggs deposited on pasture by lambs the previous year and hatch together in spring, triggered by a period of chilling over winter followed by a period of time spent between 11.5°C and 17°C.

Nematodirus Graph

Image 2 – Seasonal picture of pasture contamination of Nematodirus battus

Risks are highest when we have a particularly cold spell followed by an increase in temperature. Young lambs take in large numbers of larvae as they graze, damaging their gut, leading to profuse scouring and even sudden death. Damage is not done by adult worms, but rather by large numbers of infective larvae burrowing into the gut simultaneously.

Signs of disease may precede the appearance of significant numbers of Nematodirus eggs in the dung, making diagnosis of the condition through worm eggs counts tricky. As such, any unexplained deaths affecting lambs should be thoroughly investigated, particularly if there is also evidence of scouring. Unlike other sheep nematode worms, the larvae of Nematodirus battus develop to the infective third stage larvae (L3) within the egg.  These eggs have a double wall to allow survival on pasture over winter for over two lambing seasons and are thus much larger than other Strongyle type worm eggs. This means high survival rates for the parasite and high pressure on the farmers to deal with the issue immediately. 

Comparison: Nematodirus eggs to Strongyle eggs

Image 3 – Comparison of Nematodirus eggs to Strongyle eggs

Where possible farmers should avoid putting young lambs on fields that may have been contaminated with Nematodirus eggs the previous grazing season, particularly those paddocks previously grazed by ewes with young lambs. The good news is that lambs will develop a natural resistance to Nematodirus by 6 months of age.

SCOPS has provided a Nematodirus forecast for the last three seasons, with the help of researchers at the University of Bristol, and an improved service is available for 2016. This year the service features daily updates using weather station data, which will provide more localised, real time advice on the level of risk and the need for management action. Young lambs should be treated to prevent Nematodirus throughout the period when there is a high risk forecast for the area.

More than one treatment may be necessary at 3 week intervals dependent on the spread of ages in the group and if the high risk forecast is prolonged. Anthelmintics in the 1-BZ (white) class are still the treatments of choice for Nematodirus battus. Despite the widespread resistance of other worm species to the white wormers, Nematodirus battus remains susceptible on the majority of farms and can be used even on farms with known resistance issues in other worms. However, we must be vigilant and report suspected cases of BZ-resistant Nematodirus battus.

If you have a suspected Nematodirus case or you want to know more about how to prevent infection, contact your Vetinarian or SQP. For the latest news follow @sheep_farmers on Twitter.

For further information please see the product SPC, or contact your veterinary surgeon , SQP or Zoetis UK Ltd, Walton Oaks, Dorking Road, Walton on the Hill, Tadworth, Surrey, KT20 7NS. Customer Support 0845 3008034. Always seek the advice of your medicines provider. Use medicines responsibly (