Thin-necked intestinal worm (Nematodirus helvetianus) is often found in dairy calves in temperate winter rainfall regions. It occurs in low numbers and usually in mixed infestations with much larger numbers of small intestinal worms (Cooperia species).
Nematodirus filicollis and N. spathiger occur occasionally in low numbers in cattle but are more commonly found in sheep.
Figure 1. The egg of Nematodirus sp. is elliptical. Image courtesy of the National Centre for Veterinary Parasitology, ncvetp.org
Nematodirus species are relatively long worms 10-20 mm in length, and with slender anterior sections that are frequently coiled. Egg output is very low (about 25-30 eggs per day) and erratic despite sometimes very high worm burdens. The pre-adult worms are the pathogenic stage and cause damage to the lining of the small intestine. Disease often manifests before eggs are produced in the dung.
Further ecological information on worms and their control:
Thin-necked intestinal worms both adult and pre-adult stages inhabit the small intestine.
This parasite is usually only seen in very low numbers. Most damage is caused by the pre-adult worms producing scouring, anorexia and weakness that is evident 15 days after ingesting infective larvae. The main significance is as part of mixed-species infections.
Figure 2. The reproductive spicules and clasping bursa of a male Nematodirus sp. Image courtesy of the National Centre for Veterinary Parasitology, ncvetp.org
The only accurate way to confirm worm infections before productivity losses have occurred is to conduct a worm egg count (WEC). The eggs of Nematodirus species are large and easily distinguishable from other strongyle type eggs. The results allow you to determine the need for a drench or management action. Clinical signs usually develop before eggs are present in the dung.
However, when clinical signs are caused by the immature or pre-adult stages, ‘diagnostic’ drenching (drenching when worm egg counts are low but there is a history of favourable conditions and suggestive clinical signs) using a fully effective drench can be a useful tool. Visual responses to the drench in terms of improved condition and weight gains are suggestive of a parasitic infection.
Worm egg counting does not always correlate well with the number of adult worms present for cattle over 9 months of age. For this age group observation of physical signs such as body condition scoring and monitoring target growth weights are good additional indicators to diagnose worm infections.
If visual signs of worms are present in cattle then significant production loss has already occurred. Also, these signs can occur with other parasites and diseases.
Your decision can be assisted by using the how to decide which animals to treat section and the WormBoss cattle products search guide for your region, a simple tool that considers some of the points above. It is also important to consider cattle management options, as simply removing the affected mob to a less wormy pasture will reduce the re-infection risk.
You can also review the chemical pages on this site to find out specific information about drenches, including their drench active, drench group, how they are administered, which worms they treat, resistance status, safety information and how they work.
The negative impact of this worm can also be reduced through using one of the integrated annual worm control programs that have been specifically developed for different regions across Australia.