Horses should be wormed regularly…but NOT over wormed.

You may not always be aware that your horse has a worm infestation. A healthy horse on a good diet may not show any symptoms, so regular worm egg counts are advisable to properly manage your worming programme. If your worm egg counts are low, you can then go longer between worming treatments, saving you money and protecting your horse from ‘over worming’

Horses that are showing signs of worm infestation will typically lose weight, look a bit lethargic, lose condition and possibly cough, or start rubbing their rump and tail, depending on the particular worm that is affecting them and the seriousness of the infestation.

There are many ‘faecal egg worm count’ kits on the market to help you.

Most worms start their lives as eggs, which mature into larvae and then adults that in turn, lays more eggs. The eggs or larvae are first ingested by your horse and then continue their life cycles and migration pattern through your horse until they emerge again in your horses droppings. The cycle will now begin again. Your horse (or another horse) will ingest those eggs or larvae when he grazes on the pasture.

Managing your horses pasture can help to lower the worm burden. Regular ‘poo picking’; removal of the dung from the field is always advisable. This should be daily if possible, but as many times per week as you can manage will help. Try to keep horses with the same grazing companions and worm all horses at the same time. New horses that will be joining the group should be tested and wormed, before being allowed to graze with the herd.

Try not to overgraze your field, allowing rest periods for the pasture to recover.

There are many species of worm that affect horses in the UK. The most important ones to look out for and protect against are:

Ascarids (Parascaris equorum) or Roundworms are one of the few parasitic egg types that can be found anywhere in the environment, not just on the pasture, because they are coated with a sticky protein that enables them to adhere to all types of surfaces, such as the stable walls, buckets, troughs, fence posts etc. They can lay dormant inside their eggs for up to 10 years, being stimulated to grow once the egg has been ingested.
Once ingested, they hatch in the small intestine, where the larvae penetrate the gut tissue and migrate through the body in the bloodstream. They travel through the liver to the lungs, where they are coughed up and swallowed before travelling to the intestine. There they grow to be adults and lay eggs. The complete cycle from ingested egg to adult takes about 2½ months. Roundworms are the largest of the worms affecting horses and can grow to 15-20cm.

Roundworm  Roundworm mainly affects foals and young horses, although cases in adult and old horses have been found. Foals should not be wormed until at least 60-70 days old and it is advisable to consult your Vet before starting a worming programme. Wormers are ineffective against Roundworm until the parasite is mature. Foal manure should never be spread as manure on your pastures as fertiliser. Keeping foals in clean environment will help; scrubbing stable walls and doors, feed hay in feeders and not off the ground.

Strongyles: Large and Small

Large and small Strongyles share identical life cycles outside of the horse but behave very differently once they’re ingested.

Strongyles large worm Large Strongyles or Blood worm: This worm is transmitted almost exclusively on pasture. Eggs are passed in the faecal material, just like Roundworm eggs, but unlike the Tapeworm, which remain in egg form until they are ingested by the horse, Strongyle eggs hatch into larvae in the manure when weather conditions are favourable.  From here, they go through a series of three moults.  It’s the third stage that can infect the horse.  Under optimal conditions, third-stage larvae can live for up to three months.
For their species to survive, Strongyle must be ingested shortly after to increase its chances for survival. The larva climbs up on blades of grass where a horse can ingest it while grazing.  If not ingested it can climb back down and bury itself in the soil to wait. It can repeat this process many times until finally being ingested. This worm developed for the survival, to protect itself against adverse weather conditions and also so that if a herd migrated away from an infected area, the worm would still survive until horses passed that way again. The Strongyles are prolific egg layers.  A single horse can pass 75-100 million eggs daily.
Strongyles small worm
Small Strongyles (Cyathostomosis)
: More than 40 different species of parasites that commonly infect horses are grouped under the term “small Strongyles.” Large and small Strongyle worms, often will infect a horse simultaneously. However, horses tend to be burdened by greater quantities of small Strongyles, which also produce more eggs than the large Strongyle worms.
Small Strongyle larvae pose a significant health risk because they feed on the superficial lining of the large intestines, or the mucosa, where they cause damage that leads to the formation of ulcers, as well as severe inflammation of the colon. Larvae will migrate inside the intestinal wall and continue to develop into an adult, and live there within the mucosa in a dormant stage for an extended period of time.
Typically during the late winter and spring months, the small Strongyles migrate out of the intestinal wall into the intestines, and this massive movement of worms causes clinical signs such as diarrhoea and colic. Severely affected horses and ponies can die from a small Strongyle infection.

Pinworm (Oxyuris Equi)
Pinworms are white/grey in colour and can grow up to four inches long. The worm gets its name from their long tails which taper to a point. They are ingested like most other worms and then live in the large intestine near the rectum. The larvae feed off the mucosal lining of the intestine. When matured, the female worms they leave the gut and migrate to the anus where she lays her eggs. This is irritating and itchy for the horse, who then rubs their tails and rumps on stable walls, fence posts, trees etc. The eggs will then stick to whichever surface they have been rubbed off onto, and wait for another horse to lick them off and ingest them, and the lifecycle starts again.

Pin worm Signs of pinworm will include:
Momentary protrusion of a worm through your horse’s anus, this is when the female lays her eggs, she will then disappear back in to the rectum. An adult female can lay up to 60,000 eggs per day. The eggs will appear in a gelatinous mass around the horse’s anus.
Skin irritation and balding around the horses anus.
Tail rubbing and hair loss.Pinworm infestation should be checked for carefully and not be confused with sweet itch, mange or lice.

Tapeworm (Anoplocephala perfoliata)
There are three species of tapeworms–Anoplocephala perfoliataAnoplocephala magna, and Paranoplocephala mamillan— that can be found as adults in horses.

Tapeworm The tapeworm is different from other equine internal parasites. The tapeworm eggs are ingested by mites that live on the pasture and mature into larvae. The mites are then eaten by the horse while grazing. The larvae are then released and travel to the horses gut where they live where the large and small intestines meet.  The females don’t lay eggs, but begin to shed segments full of eggs around six to eight weeks later. The segments containing eggs break off from the tapeworm and are passed in the manure. These are
ingested by the might again and the cycle starts again.

Bot (Oestridae family)
Bots are internal parasites, but they are not worms. They are the larval stage of a fly,.About the size of a honeybee, these hairy brown flies dart around the horse and glue their tiny eggs to the hairs of the horse’s legs, and flanks. The horse licks and ingests the eggs; this licking and chewing likely is what causes the eggs to hatch. The larvae spend a short time–about three weeks–in the lips, gums, or tongue before migrating and attaching to the lining of the stomach or small intestine.
Bot larvae spend the winter in the host and live in the gut for about seven months before being passed into the environment in manure. The larvae enter the soil, where they pupate and emerge as adults (flies) to lay eggs.
A Bot knife should be used to remove eggs from your horses coat before they are ingested. Stroking the bot knife across the eggs will remove them.

Bot fly The Bot fly Bot egg Bot eggs on the horses coat

 

Useful links
http://www.bhs.org.uk/~/media/BHS/Files/PDF%20Documents/Worm%20Control.ashx
http://www.westgatelabs.co.uk/info-zone/worming-programme.htm
http://www.intelligentworming.co.uk/doyouknow-aboutworms-pinworms.asp


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