5. Tape Worm (Anoplocephala species) The most common tape worm in the UK is called Anoplocephala perfoliata.
Infection is relatively common with younger and older animals more commonly infected.
The tape worm has a complicated life cycle which involves an intermediate stage in the forage mite.
Adult worms live at the junction of the small and large intestine where they can cause thickening and ulceration of the gut wall (Fig. 7).
Infection can also disrupt gut motility and both spasmodic colic and small intestinal impaction have been shown to be associated with tape worm infection.
Diagnosis of tape worm infection can be challenging as eggs are shed inconsistently in the faeces; however, a blood test to identify tape worm proteins is now available which is more reliable.
Many people simply prefer to treat once or twice a year for tapeworms rather than test for their presence.
There are two products available for treatment of tapeworms: a single dose of praziquantel (eg Equitape) or a double dose of pyrantel (Strongid P).combination worming products are also available eg praziquantel combined with ivermectin in Equimax and with moxidectin in Equest Pramox. Fig. 7: Junction of the small and large intestine of a horse showing large numbers of adult tape worms. 6.
Strongyloides Westeri This worm only affects foals as immunity develops by approximately 6 months of age.
Foals can be infected by ingesting larvae from the pasture or milk from the dam and by larvae on the grass penetrating the foal’s skin.
Adult worms live in the small intestine and heavy burdens can cause diarrhoea, weight loss, dullness and reduced growth rate. Foals can be treated for Strongyloides westeri using any wormer, except moxidectin which is not licensed in young stock (less than four months). 7.
Bots (Gastrophilus species) ‘Bots’ are the larvae of a fly which is active in the summer months.
The fly lays eggs on the legs of the horse which are then eaten whilst the horse grooms its legs.
The larvae develop in the stomach and bots are passed in faeces during summer months.
It is questionable whether bots actually cause disease.
Ivermectin and moxidectin products kill bots and, if used for bots, are best given in the winter when there are no further flies to lay eggs.
What is the Best Worming Protocol? Over the last decade resistance has been reported, particularly in cyathostomin populations, despite use of an increasing number of wormer drugs.
This is worrying as there are no new drugs in the pipeline if worms become resistant to all the currently available drugs.
There are several different ways which horses can be de-wormed, each with pros and cons.
Interval Dosing ‘Interval dosing’, which many horse owners / yard managers use, and is promoted by drug companies, involves regular wormer administration based on the egg reappearance periods after treatment with wormer: eg dosing with moxidectin (Equest) every 13 weeks as this is how long it takes for eggs to reappear in the manure after treating with moxidectin.
It is important to realise if using this method that the egg reappearance time differs for each wormer drug: moxidectin 13 weeks, ivermectin 8 weeks, pyrantel 6-8 weeks and fenbendazole 4-6 weeks.
This is an ‘easy’ protocol to follow; however, this regimen will result in the routine worming of many horses that do not need it as studies have shown that in any given population, 80% of worms are carried by only 20% of horses.
Not only is this a waste of money and giving your horse unnecessary drugs, more importantly this ‘over-worming’ is believed to have made a substantial contribution to drug resistance.
Strategic Dosing This protocol involves worming horses at key times when parasite burdens are thought to be highest eg larvicidal treatment of encysted cyathostomins in winter.
Although this provides a more rational approach, problems can arise when abnormal patterns of weather lead to early or late peak pasture counts or when heavily infected animals are added to the population.
Targeted Strategic Treatment This protocol adapts the strategic dosing programme to administer wormers at the most appropriate times of the year, based on the life cycle and environmental factors involved (eg pasture management), and also takes into account the levels of infection in individual horses by monitoring individual faecal worm egg counts (FEC).
This means that each property has its own individual treatment plan according to the horses and factors relevant on that particular property.
Regular FEC are used to identify the horses most susceptible to worms and that are contaminating the pasture.
These horses are de-wormed whilst the other horses are left untreated to reduce the use of worming drugs (and therefore the likelihood of resistance) on the property.
This type of programme is typically associated with a substantial (>50%) reduction in the total amount of wormers used on a yard.
If using this programme it is important to remember that FEC detect only adult worms and therefore a larvicidal product should be used in all grazing horses, once per year, regardless of FEC results. Likewise, horses should be treated once per year for tapeworms (remember these can be combined using a combination wormer if desired).
Management Practices An essential part of all worm control programmes is to ensure that drug treatments are combined with good management to minimise infection levels and consequently reduce reliance on drugs: 1.
Do not overstock 2.
Remove faeces regularly from pasture (twice weekly) 3.
Give wormer doses based on the weight of each animal 4.
Quarantine newcomers for 48 hours and treat with moxidectin (preferably combined with praziquantel for tapeworms) 5.
Co-grazing with sheep or cattle reduces pasture contamination 6.
Harrowing in the summer (not winter!) can also be used to limit pasture contamination If you have any queries regarding worming your horse or wish to set up a targeted strategic worming programme, call us at the Dick Vet Equine Practice on 0131 445 4468
Read more about Bots (Gastrophilus species) ‘Bots’ are the larvae of a fly which is active in the summer months: