1. Elliott Clifton BVSc MRCVS
Worming your horse.
Elliott Clifton BVSc MRCVS

2. Worming Worming advice can be confusing and controversial
Blanket treatment is outdated
Strategic and targeted approach needed
Resistance issues important

3. The Worms Nematodes Cestodes Lungworm Large Redworm Pinworm Tapeworms
Worms (Helminths)
Nematodes
Cestodes
Lungworm
Large Redworm
Pinworm
Tapeworms
Small Redworm
Roundworm
Threadworm

4. Probably the most common worm in our horses Over 40 different species
Small Redworm (Cyathostomes)
Probably the most common worm in our horses
Over 40 different species
The larvae of these worms hibernate (encyst) in the large intestine wall
Emergence of these larvae can be fatal.

5. These worms can be serious
Large Redworm (Strongyles)
These worms can be serious
There is extensive larval migration within the abdomen
Their lifecycle can be 6 – 11 months long
Rapid weight loss, diarrhoea and potentially surgical colic
Rarely become clinical because of regular worming now.

6. Typically affects foals Complete lifecycle can take place on pasture
Threadworm (Strongyloides westeri)
Typically affects foals
Complete lifecycle can take place on pasture
Diarrhoea is the prominent clinical sign
Natural immunity is usually present at 6 months of age.

7. Eggs can survive in the soil
Roundworm – Parascaris equorum
Can be up to 50 cm in length!!
Eggs can survive in the soil
Greatest risk is 6 months to 2 years of age
Respiratory signs as well as diarrhoea and weight loss.

8. Donkeys are the main host Horses can’t complete the lifecycle
Lungworm (Dictyocaulus arnfieldi)
Donkeys are the main host
Horses can’t complete the lifecycle
Respiratory signs

9. Pinworm (Oxyuris equi)
Adults live in the colon (large intestine)
Females deposit eggs around the anus
Causes intense itching.

10. Oribatid (forage) mite is intermediate host
Tapeworm (Anoplocephala)
Oribatid (forage) mite is intermediate host
Adults live in small intestine and caecum
Infestation can cause intususception or food impaction

11. Bots (Gastrophilus) Their lifecycle takes one year
Migrate through horses mouth and latch onto stomach wall
Can cause inflammation of oral cavity and contribute to gastric ulcers

12. Adults live in the nuchal ligament for years..
Neck Threadworm (Onchocerca cervicalis)
Adults live in the nuchal ligament for years..
Larvae cause severe itching and skin reaction
Can cause ocular disease
Spread by biting insects (midges)
Climate change?

13. Stomach Worm (Habronema)
Attach to stomach wall
House and stable fly intermediate hosts
Can cause severe wounds and gastritis (inflammation of stomach wall)

14. RESISTANCE!!!
Ability of parasites (organisms) to survive a dose of treatment which would normally be effective
Resistance to fenbendazole (Panacur) well documented
Some evidence of resistance to avermectin wormers
Worm-free horses do not help the issue of resistance
Refugia is important

15. Faecal Worm Egg Counts
20% of the horse population will be infested with 80% of the worm population of that pasture
Faecal worm egg counts detect eggs produced by worms except tapeworm, pinworm and bots.
Just a ‘snapshot’ of the bigger picture
Fresh sample, keep it cool, deliver it same day to lab/vets
A count of <250 epg does not necessitate treatment
Faecal egg count reduction tests to monitor treatment effectiveness and resistance
Save money in the long run!

16. Testing for Tapeworm
Can test antibodies to tapeworm in blood or saliva
Saliva test easy to use and quick results – doesn’t need a vet to do
Blanket treatment not necessary in a lot of cases
Results have to be interpreted with care
Tests can’t be use to assess wormer efficacy

17. The encysted stages cannot be detected using any test at present
The encysted Cyathostomes
The encysted stages cannot be detected using any test at present
The recommended time of treatment is between November and February – this is typically when larvae ‘hibernate’
Once a year dosing for the encysted stages reduces resistance

18. Tetrahydropyrimidines
The Drugs...
Ivermectin
Moxidectin
Avermectins
Benzimidazoles
Tetrahydropyrimidines
Fenbendazole
Pyrantel
Praziquantel

19. Don’t treat March/April TREAT May/June Same as above Same as above
‘Gold Standard’ Protocol
Don’t treat
<200epg
March/April
Worm egg count
TREAT
>200epg
Test for tapeworm?
May/June
Worm egg count
Same as above
Worm egg count
Same as above
August/September
Test for tapeworm
Treat/don’t treat using Praziquantel or Double dose Pyrantel
Treat for encysted cyathostomes
November - Feb
Treat for bots

20. How heavy are your horses??
Holistic Approach
Poo Pick
Co grazers
Where’s the muck heap?
Avoid ‘dose and move’
Avoid overstocking
Harrowing??
How heavy are your horses??

21. QUIZ!!! What is PSSM an abbreviation of?
Which worm can encyst in the large intestine gut wall?
What disease can the ingestion of sycamore cause in horses?
Which famous actor is the president of the British Horse Society?
When was the Shire Horse Society set up a) 1870 b) 1901 c) 1884?
Which drugs are effective against tapeworm?
What is PSSM an abbreviation of?

22. QUIZ!!! What is the normal heart rate of the horse?
What is the proper name for the equine pinworm?
How high is the world record for the highest jump jumped by a horse and rider?
What is the trade name for Fenbendazole?
How far can worm larvae travel from a muckheap?
What is the medical name for the disease responsible for a ‘roarer’?