Intestinal and other worms can become a problem for horses under modern management systems. Many worms pass their eggs in the faeces of horses, and the eggs or larvae of the worms are then ingested as the horses graze. Other parasites such as bot flys lay their eggs on the horses legs and body where they are ingested by the horses as they groom.
Preventing worm infestation
By looking at the way worms infect horses it makes sense that to decrease the chance of our horses getting worms we should follow the following steps:
- Reduce contact with infective larvae by collecting faeces from pasture at least weekly if possible.
- If it is not possible to collect faeces pasture management such as cross grazing pasture with cattle or sheep (most worms are species specific i.e. horses will not get cattle worms and cattle will not get horse worms), grazing young horses on ‘cleanest’ pasture, use of faecal spreaders and taking advantage of climatic changes such as cold winters or hot dry summers to kill worm eggs by cold or drying.
- Place feed and hay in bins, not on the ground.
- Reduce fly or insect born worms by good fly managment- keeping areas where there are horses kept clean, use of short or long acting fly repellants, use of rugs.
- Reduce bot infestations by regular removal of bot eggs from the horses (using a bot knife or similar).
- Do not keep horses with donkeys unless the donkeys are known to be free of lungworm.
- Note this is at the bottom of the list- targeted use of anthelmintics (wormers).
Assessing worm infestation
The eggs of many of the worms are spread in faeces, so one of the most valuable tests available to us for determining worm infestation in horses is the use of a faecal egg count. Faecal egg counts invole diluting a sample of faeces in a solution and allowing the worm eggs to float to the top of the sample. Part of the sample is then transferred to a microscope slide and examined for worm eggs. The eggs of some of the worms appear very similar, so it is also possible to allow the eggs to hatch and then examine the larvae to determine the worm type (for this a sample needs to be sent to an external pathology lab).
If you would like a faecal egg count for any of your horses please call us and we can give you directions on collecting the sample from your horse(s). If you bring the sample to the clinic we can run the test for you.
If no worm eggs are found your horse may not need worming.
The faecal egg count is also a simple way of assessing whether your worming program is effective. If a faecal egg count is performed prior to worming, then 2 weeks after worming there should be a significant decrease in the number of worm eggs found after drenching compared to before.
What worm product should I use?
There are a lot of worm products available on the market, however most wormers can be broadly placed into groups:
– The ‘BZ’s’: the benzimadazole group includes oxfendazole, oxbendazole, fenbendazole. There are multiple strains of resistant worms in Australia to the ‘BZ’s’, especially small cyathastomes.
– The ‘BZ’s’s are often combined with Morantel or Pyrantel to reduce the level of resistant worms to treatment, and to treat tapeworm infection.
– The ‘Mectins’ (macrocyclic lactones): the ‘mectins’ were released approximately 20 years ago and had a significant effect on controlling worms in horses and other species. Unfortunately there is evdience of resistant strains in some worms in Australia. The ‘mectins include: ivermectin, abamectin and moxidectin.
– Praziquantel: effective against tapeworm