Links veterinary Group Horse Wormer Information

Why worry about parasites in my horse?

Nearly every horse alive will have one or more intestinal worms. In a proportion of horses this small population can increase and cause clinical problems such as colic and serious diarrhoea. For example the University of Liverpool has demonstrated a strong correlation between tapeworm infestation and risk of colic.

Diarrhoes is most often caused by larval forms of the small reworm (cyathostomes) and is mostly seen in young horses in the Spring but also in older or infirm horses over the winter. These larvae cause damage to the gut wall when they come out of a state of 'hibernation' and this damage leads to diarrhoes, weight loss and in extreme cases death.

How do I control parasites?

This is always a three pronged approach:

Use of horse wormers

Reducing environmental levels

Monitoring levels of infection

Use of horse wormers

This can be done in several ways.

Interval dosing means using a horse wormer at regular intervals throughout the year. This can be expensive and sometimes leads to overuse of horse wormers when not strictly necessary. Also the seemingly excessive complexity of regimes used by some establishments makes a potentially complicated disease control programme absolutely beyond comprehension!

Strategic dosing involves the use of specific horse wormers at specific times of year in order to break the seasonal cycle of the parasites. This can be problematic if seasonal conditions change and alter the worm burden and also if heavily infected horses are added to the group.

Targeted dosing is the use of horse wormers only when parasite levels (measured by faecal egg counts or blood ELISA) dictate this to be necessary. Unfortunately the larval stages of the cyathostomes for example dont often show high faecal levels so this can be problematic.

The Links Veterinary Group can advise on the best horse worming strategy for your horse. One of the most common methods used is a combination of interval dosing and strategic dosing whereby twice yearly tapeworm treatment is combined with a broad spectrum wormer (which shows activity against mucosal cyathostome larvae) every three months.

Reducing envronmental levels

This is basically good pasture management to reduce the exposure of grazing horses to infectious material.

Pastures should be cleared of droppings twice a week - this can have a dramtic effect on reducing levels of parasitism. Pastures should be regularly 'rested' to allow the worm eggs present to die off. This should be no less than 3 months without horses present. Mixed grazing using cattle and sheep can have a good effect on reducing contamination as these species take up the eggs present but dont become infected by them and so produce no equine parasite eggs in their droppings.

Stocking density should also be carefully monitored and this means no more than 1 or 2 horses should graze per acre of grass.

Monitoring levels of infection

Faecal egg counts oare regularly used to monitor parasite levels. The test is useful to check new horses, to ensure worming programme is working, to investigate illness and to identify particulaly high 'shedders' of worms. However the test does not pick up larval forms and can does not differentiate between certain worm types.

A blood test can be used to show antibody levels against tapeworm which again can be used to monitor worming programmes, check new horses and investigate illness (colic specifically). Limitations of this test chiefly reflect the fact that antibody levels to tapeworms stay increased in horses for up to 4 months so a high level today may actually reflect increased infection some months ago.

At the Links Veterinary Group we would advise a faecal egg count to be performed on new arrivals before mixing with current horses, and also a tapeworm ELISA blood test in cases of recurrent colic.

Some modern wormers may well also be indicated for the control of other conditions such as mange mites or lice and also for the winter erradication of stomach 'bots', the pupae of a fly which can cause stomach ulceration and in rare cases stomach perforation with fatal consequences.