How to Control Parasitic Worms

What is a Parasitic Worm?

Gastro-intestinal parasites (worms) affect all horses and ponies and include various species of nematodes (which are slender segmented worms). The definition of a parasite is an animal or plant living in or on another and drawing nutriment directly from the host.
Parasitic worms damage the intestines, as they attach to the inside of the gut, suck blood and burrow through the body of the host during the migratory part of their life cycle.

The Life Cycle Of A Worm

The eggs, which are passed out in the dung, undergo a period of incubation of several days. The infective larval stage hatches from the egg, under ideal conditions this is within about a week. The larvae migrate in the water film over the surface of the plants and spread themselves through the grass around the droppings. From here, a suitable host (e.g. your horse) must eat them. They can then develop into the adult worm.

Development of most species is slowed or halted by winter temperatures, (assuming we have some cold weather and frosts). Dry weather causes the death of some larvae and their movement to edible grass is slowed without the water film on the grass.

The following table summarises the different species of worms!
Type Species Incubation -Larvae Incubation - Adult Large strongyles (Redworms) Strongylus vulgaris Intestine Arteries Liver Caecum Colon Small Strongyles Trichonemaspp. Intestinal wall Caecum/Colon Ascarids (Roundworms) Parascaris Equorum Liver/lungs Small Intestines Threadworms Strongyloides Westeri Various tissue Small Intestine Pinworms Oxyuris equi Intestine wall Colon/Rectum Lungworms Dictyocaulus arnfieldi Lungs Bronchi of lungs Tapeworms Anoplocephala perfoliata Intermediate host (mites) Small Intestine/caecum Bot Gasterophilus spp Stomach Gadfly (insect)
Reducing The Worm Burden Environmental and management factors can directly influence the development and survival of the worm population on the grass. Combined with an efficient worming programme, this can greatly reduce the threat of harmful parasitic infestation. One way to reduce the worm burden it to start with a 'clean' pasture, this is especially important when the larvae population is high, during the spring, summer and autumn. Large numbers of larvae on the grass coincide with the best growing conditions for grass (warm and wet). This is when most horses spend the majority of their day grazing. Land that has not been grazed since the previous autumn and has been harrowed, rolled and fertilised, then been cut for hay/silage is the 'cleanest'. If the grass is grazed in the spring, then topped, harrowed and fertilised; left to rest for 6 weeks and then grazed by cattle or sheep this will also help to reduce the worm problem.
Cattle prefer longer grasses and are therefore more suitable to graze with horses than sheep; they will also eat grass that horses avoid. Sheep will eat the docks but graze the grass very short. Larvae eaten by cattle or sheep will be destroyed as both cattle and sheep are ruminants.
	Picking up dropping from the paddock is vital, this job should be done at least twice a week, but daily is more advisable and also less of a chore. Two horses in a field skipped out daily take about 20 - 30 minutes, plenty of time to observe your horse.
Worming your horse 24 hours before turning out into fresh pasture will also help to keep the paddock 'clean', and making sure that you collect all the dropping produced will greatly reduce the worms in the paddock. When purchasing a new horse, keep him/her isolated from any other horses until your vet has done a faecal count and the horse has been wormed accordingly.
Finding Out About Your Horse's Worm Burden By counting the number of eggs in a few balls of dung your veterinary surgeon can find out about yours horse's worm burden. The vet can then advise you as to how much and of what brand of drug to use to eliminate the worms. Subsequent egg counts done 10 to 14 days after the initial treatment will reveal whether the treatment has been successful or whether the worms have developed a resistance to the drug used. Resistance occurs partly because owners worm without expert advice, using incorrect amounts of drugs and at the wrong intervals. This creates a breed of resistant 'super-worm' that can cause major problems. The parasitic worm has a very efficient life cycle and has been around for as long as there have been horses. We cannot eradicate the worms' only keep it under control with good pasture management and regular doses of anthelmintic wormers.

Comments

If you have a specific tip, experience or comment relevant to this article please post a comment below. We are unable to answer individual questions through the comments system. The New Rider Message Board is a better place to post specific questions.

marie   29th Oct 02 What happens if everyone in your yard is not worming their horses and they are all turned out to the same paddock. Is my horse protected by her own worm programme in these conditions. I am in a DIY yard and there is no work programme in operation. The 25 acre turn out is never cleaned or rotated so there are years and years of worms there. Any solutions?

Add Your Own Comment

Sorry, the comments facility is turned off for maintenance.

Library Index