Parasites usually target a specific species, but not so Trichostrongylus axei, or the stomach hair worm.
Trichostrongylus can infect sheep, cattle, goats and horses.
In fact, Trichostrongylus is the only worm that horses have in common with these species.
The adult worm is small – only about half a centimetre long – and they generally don’t cause horses major problems.
Horses become infected with this nematode by eating grass infected with eggs. The ingested eggs hatch and the larvae take up residence in the stomach where they mature and lay more eggs, which are passed out in the manure to continue the life cycle.
The adult worms can cause irritation to the finger-like villi that line the gut and damage the tiny blood vessels. Heavy infestations can trigger dark, foul-smelling diarrhoea and can limit the ability of the horse to gain nutrients from its food due to damage to the gut lining.
Foals are more likely to suffer heavy infestations than adults.
It would be tempting to think that rotational grazing horses with cattle, sheep or goats is not a good idea.
This is not the case. The risk of Trichostrongylus infection is far outweighed by the benefits of sheep, cattle and goats eating – and killing – the infective larvae and eggs of much tougher foes, such as strongyles.
Trichostrongylus are far less of a problem in mature livestock, so if you can rotate older sheep and cattle through your paddocks, the chances of a major problem are small.
Trichostrongylus can be killed with several drenches, including the tried and trusted macrocyclic lactones, which include ivermectin and moxidectin.
If you have an effective worm-management programme in place, the stomach hair worm is unlikely to have you pulling your own hair out.
First published on Horsetalk.co.nz in February, 2009