Parasitic worms live in the intestines of horses and ponies. Small numbers of worms can be tolerated causing no effect on well being. However large worm burdens can cause a range of problems including: Ill thrift, diarrhoea, colic, DEATH. It is therefore extremely important to have a suitable worming programme in place for your horse.
Types of Worms
Small redworms (cyathostomes)
Larvae ingested from grass, live in lining of large intestine, can go into hibernation in the intestine wall (encysted larvae), emergence from the bowel typically in spring causing severe diarrhoea.
Large redworms (strongylus)
Larvae ingested from grass, migration of larvae through the blood vessels of the intestine and liver, cause inflammation and obstruction of blood vessels resulting in damage to intestine.
Typically affect younger horses, eggs develop into larvae and migrate through other organs such as the liver and lungs before returning to the small intestines to develop into adults.
Live at the junction between the small intestine and caecum, mites on the pasture act as the intermediatic host for transmission allowing the tapeworm to complete its cycle, can cause colic, weight loss and diarrhoea.
Larvae of adult bot fly, horses lick eggs from legs and ingest them, can cause ulceration of the stomach wall
Types of wormer and when to use them
Kills large redworm, small redworm, pinworms, large roundworms, lungworms, threadworms and stomach worms. Dosing interval 8-10 weeks. Single dose given in May, July and December. Eqvalan.
Kills tapeworms. Single dose given April/May then September/October. Can be used alongside any wormer treating routine worms. Equitape.
Ivermectin & Praziquantel
All the benefits ivermectin with added tapeworm control. Single dose in Spring and Autumn (March/April and September/October) for roundworms and tapeworms. Eqvalan Duo or Equest Pramox.
Kills small redworm including encysted stages, large redworm , pinworms, large roundworms, intestinal threadworms, stomach worms and bots. Dosing interval for small redworm 13 weeks. Single dose in winter to treat encysted small red worm. Equest.
Kills large redworms, small redworms, large roundworm and pinworms. Can be used at a double dose to kill tapeworm. Dosing interval every 4-6 weeks during summer and autumn. Pyratape P.
Worm Egg Counts
Treat for worm threats as they arise, keep an eye on worm population with worm eggs counts (WEC). These can be carried out over the summer grazing period every 8-10 weeks after your horse's last dose in April/May.
If your horses WEC is < 200 epg then worming in not required and another WEC should be carried out again in 8-10 weeks (this process is repeated throughout summer, worming when needed) WEC however do not detect tapeworm or encysted small redworms.
If you treat your horse when it is not needed this may result in the survival of only the treatment - resistant worms. Overtime these breed and begin to out number the sensitive worms. With a population consisting of only resistant worms worming treatments become ineffective and parasites cannot then be controlled leaving horses prone to all the health problems associated with large worm burdens.
Refugia is the population of worms that can still be affected by wormers and the more of these worms we have the smaller the proportion of resistant worms.
Dosing: Ensure you have an accurate weight for your horse. This can be achieved using a weight tape or a weigh bridge. Giving too small a dose of wormer increases the risk of resistance as the worms are exposed to treatment at a dose that doesn't kill them but allows them to develop resistance. Too large a dose gives no additional benefit.
Poo-picking at least twice a week is one of the most effective ways to control worms. Parasites on the pasture are ingested by grazing horses. Removing the droppings is a good practical way to reduce pasture contamination.
If you have any questions regarding worming your horse or you would like your own personal worming planner please contact your local practice.