Nematodirus- an under-rated parasite

E-mail contact: Dr Ray Batey

Austbreed's veterinarians are contactable through: frontdesk@austbreed.com.au

or visit our website: http://www.austbreed.com.au

There are two Nematodirus species ('thin-necked intestinal worms') which play a role in parasitic disease among sheep in temperate parts of Australia and other parts of the world.

The characteristic eggs of these worms can be found in the faeces of mainly young sheep on many farms, but usually not in numbers which would indicate a problem. However, this can be deceptive because these parasites are intermittent egg producers, with some individual sheep having large numbers of adult worms but few eggs in the faeces.

As well as being different in appearance, the eggs and larvae of Nematodirus are extremely resistant to drying AND to very cold conditions, such as frosts or even snow. There is a strong suspicion that larvae within eggs may survive many months over the hottest summer and be available to the sheep as soon as it rains in late autumn under Western Australian conditions.

Unlike many other worms, the larvae do not expend energy swimming in the moisture film on blades of grass or the leaves of other pasture plants, but are picked up when animals graze close to the ground.

Our experience is that this parasite may have significant effects at any time of the year, usually when it is least expected and when other intestinal parasites are not causing a problem. Sometimes there is another problem simultaneously such as a nutritional stress or deficiency, which may mask the effects of Nematodirus.

Examples of Nematodirus problems we have encountered with clients' animals include:

• Suckling lambs with concurrent cobalt deficiency,
• Young (hogget) sheep grazing very close to the ground during prolonged cold periods in early winter when pastures are not growing,
• Heavily stocked adult wethers rotationally grazing irrigated pastures,
• Weaner sheep when unseasonal rain in early summer has prolonged a green pick underneath the normal dry feed,
• Non-lactating ewes when there has been early autumn rain but no follow up.

Our experience is that there are no consistent 'symptoms'. Animals with heavy Nematodirus infestations are often listless with perhaps soft faeces (often NOT diarrhoea). In Western Australia, this can occur at times when other conditions including deficiencies may produce similar signs. Some animals just lie down and die! We have also encountered adult sheep with pure infestation of Nematodirus, which have developed 'bottle-jaw' (due to protein deficit) which was initially thought to be haemonchosis (barber's pole worm) until it was investigated!

Assessing the significance and developing control and treatment strategies for Nematodirus requires a thorough investigation by a veterinarian.

IMPORTANT: Routine strategic drenching is often not a solution or guarantee that the parasite will not emerge, particularly in view of its prolonged survival on the ground. Please contact us or your local veterinarian for further advice.