Worm control is vital in horses, as significant worm burdens can cause colic, diarrhoea, weight loss and poor performance.
There are several ways to approach worm control in your horse:
1) ‘Interval dosing’; a specific drug is given at regular time intervals during the year
2) ‘Strategic dosing’; a method widely and successfully used in cattle and sheep
3) ‘Targeted strategic dosing’; only horses with a proven worm burden are treated, thus reducing the incidence of drug resistance
Worms can develop resistance to worming drugs in the same way bacteria can develop resistance to antibiotics. At present in the UK, there is widespread resistance to the benzamidazole group of drugs. We can help to delay resistance in other groups of drugs by using them responsibly and only when required. Diagnostic tests such as faecal egg counts and blood samples can help us to do this.
When deciding which worming regime is right for your horse, several issues must be addressed:
Are the horses on the yard managed by one person, or are there several owners?
For a worming regime to be most effective, all horses in the yard should be included in the programme
- What ages are included in the population? Young horses are more likely to develop high worm burdens; these cause clinical disease and contaminate pasture with infective stages of parasites
- Is there any history of parasite-associated disease?
- What is the worming history of the horse?
- What are the pastures like? Over-stocked, heavily grazed pastures, where muck is never removed, are more likely to result in high worm burdens
In some cases interval worming is the only safe option; for example if a horse is kept on a yard where each owner has their own protocols about worming.
However, for many horse owners a targeted worming programme can be practical, cost-effective and help reduce the incidence of drug resistance.
To implement a strategic targeted worming regime, a muck sample is taken from each horse in the yard. Using a microscope, we count the number of worm eggs present. This allows us to identify and treat only the horses which have a moderate worm burden, reducing the use of wormers. This should initially be carried out every 3 months, then every 6 months once a pattern of infection is established. Tapeworms can also be a problem in horses, causing recurrent colic. To detect levels of tapeworm infection, a blood sample is taken, and a laboratory test carried out which detects antibodies; the body’s natural immune response to tapeworms. A blood sample should be taken once a year by your vet. Again, only infected animals require treatment.
The benefits of a targeted strategic control programme include:
- Cost effectiveness; as worming drugs are only used in horses with proven infection, the expense of treating non-infected horses is saved. In many cases, the cost of the diagnostic tests is more than covered by savings on worming drugs
- Environmentally friendly; residual activity of wormers in horse faeces can kill invertebrates and insects on the pasture. Targeted use of drugs limits this harmful effect
- Risk of resistance to worming drugs reduced; a lower level of use reduces the risk of resistance developing
Not all parasites can be picked up using diagnostic tests. Cyathostomes (small redworms) can ‘hibernate’ in the gut wall, only to re-activate in spring. These stages are very resistant to most worming drugs, with a 5 day course of Panacur Equine Guard or a one off dose of Equest being effective treatments. This should be carried out at the end of the grazing season every year, whatever worming regime you are using.
Interval worming can also be used. This is ideal in large livery yards, where each owner has their own worming protocol. 3 groups of wormers exist, and you should stick to one of these groups for 1 whole season before rotating to another group. This will help to slow down resistance to drugs. The groups are:
- Panacur Equine Guard Use 6-8wks One bottle per 600kg
Panacur Granules Use 6-8wks One sachet per 300kg
- Eqvalan Paste Use 8-10wks One syringe per 600kg
Equest Gel Use 13wks One syringe per 545kg
- Strongid P Use 4-6wks One syringe per 600kg
Equitape, Equimax or Strongid P should be used in March and October to treat tapeworms, whilst a 5 day course of Panacur Equine Guard should be used at the end of the grazing season to treat hibernating small redworms. This can also be used for new arrivals with an uncertain worming history.
Whatever worming regime you use, pasture management is another vital component. The main principle is to reduce pasture contamination, preventing the worms from completing their life-cycle in the horse. Droppings should be removed from the pasture twice a week. If it is practical, pasture rotation can be used; allowing a field to ‘rest’ for 3 months will kill eggs and larvae. Mixed species grazing can also be used, as sheep and cattle will eat larvae and eggs that they aren’t susceptible to.
To take advantage of our faecal egg count service:
- Collect a small amount of your horse’s muck; we only need 3g of muck to carry out the egg count. Please ensure the pots are clearly labelled if you are bringing in multiple samples
- Drop the sample off at the surgery
- We will contact you once the egg count has been carried out. One of our vets will advise as to what action should be taken.
Blood samples for tapeworm ELISA can be taken at your horse’s annual vaccination booster. A small sample is taken from the jugular vein, and is then sent for analysis at Liverpool University. Once we have the results, a vet will be in contact with you to interpret the results and advise you on any action to be taken
A tapeworm ELISA (when blood sampling is carried out at a booster vaccination or at any other visit) will cost £25 (including VAT)