Friday, 1 May 2015

All About ....... Worming

Following on from last week's blog which concentrated on the 'science bit' about worms today I wanted to cover worming (or de-worming).

Why worm?

To maintain a horses health and performance it is essential that the worm burden is controlled. To do this an effective worm control programme is essential and the aim of this programme is to break the lifecycle of the worms.  

Worms can cause:

  • Loss of condition such as weight loss, dull coat & lethargy 
  • Loss of performance 
  • Diarrhoea 
  • Colic 
  • Sometimes even death


Over the centuries the treatment for horse worms have developed and changed.  From Garlic in ancient times, through blood-letting in the 1600's, to the first licensed chemical wormers introduced in the 1960's.  The chemicals are basically toxic to the worms but initially were also toxic  to the horse.  Different chemical groups were developed, first thiabendazole and then the group known as benzimidazoles.  More recently Ivermectin, Pyrantel and Moxidectin.  Resistance to benzimidazole wormers first appeared in sheep and then in horses across multiple worm species in the 1970's.

What is Resistance?

Resistance is the ability of some worms to survive a dose of wormer which would usually be lethal to them.  Beginning with a small number they will pass the resistance on to their offspring and so the resistant population will grow if left unchecked.

Worming Routines

In the late 20th century seasonal rotation of worming was recommended to minimise the increase in resistance.  This meant that wormers were given at specific times of the year, in line with the parasitic worms most common at that time of year.  It was recommended that the chemical was rotated and not just the brand and that worming was carried out every 8 - 10 weeks depending on the chemical.  

Unfortunately resistance in all species of parasitic worms and to all chemical groups has continued to grow.  Now we are recommended to use a Targeted Worming Routine based on Faecal Worm Egg Counts (FWEC).

This is when I begin to find it a little confusing. 

  1. Do we worm at all? 
  2. Do we worm at specific times of the year? 
  3. Do we avoid certain chemical groups? 
  4. Do we worm for everything at once? 
  5. Do we worm for a certain type of worm? 
  6. What is a FWEC?
  7. When do we do FWEC? 
  8. How often do we do FWEC? 
  9. Do these FWEC test for everything? 
  10. What is a Tapeworm test? 
  11. How do we do these tests? 
  12. What if our FWEC are constantly so low we don't need to worm? 
  13. How do we know what to worm for? 
  14. How do I accurately worm my horse?   

Do we worm at all? 
YES.  FWEC are not able to detect Encysted Small Redworms - which are the dormant Small Redworms - if these are not controlled and they then emerge in large numbers they can cause severe health problems. FWEC also are not able to detect Bots or Tapeworm but there is an alternative test for Tapeworm.

Do we worm at specific times of the year?
YES.  We should all worm for the Encysted Small Redworms in the late Autumn or Winter.  In addition, during the Winter we should worm for Bots.

Do we avoid certain chemical groups?
The chemical we use will be affected by the worms we are targeting as some are more effective than others.  It would seem sensible to choose the chemical group which has shown the least resistance over recent years but that is still effective. 

Do we worm for everything at once?
No.  This is a new idea but the recommendation now is that we ONLY worm for the species of parasitic worm which we need to target.  The worms we need to target will be shown in our FWEC or in the late Autumn/Winter we should target Encysted Small Redworm and Bots.

Do we worm for a certain type of worm?
YES.  See previous answer.

What is a FWEC?
my blog here.

When do we do FWEC?
Throughout the Spring/Summer/Autumn.  In the Autumn and Winter fewer worms develop and they begin to hibernate in the intestine.  FWEC are less effective in the Winter because there are far fewer worms passed out in the droppings.  

How often do we FWEC?
The recommendations seem to vary for this between every 6 weeks and 3 months.  It seems sensible to carry out one in the early Spring and then one every 8 weeks until the Autumn.  This will mean 4 in a year.  If your horse consistently has low or 0 egg count then you can FWEC less often ie: 3 times - Spring, Summer, Autumn!  If your horse has a high count then increase the frequency of testing for a while.

Do these FWEC test for everything?
No. As mentioned above FWEC are not able to detect Encysted Small Redworms, Bots or Tapeworm but there is an alternative test for Tapeworm.

What is a Tapeworm test?
The test for Tapeworm is a saliva test, I uploaded a
'How to ...' video about this. Using a swab you collect saliva which is then tested for a salivary antibody which is specific to Tapeworm.  If your horse shows a borderline or high result then worming is recommended. These tests should be conducted when we would normally worm for Tapeworm ie: Spring and Autumn.  The test should not be done if the horse has been wormed for Tapeworm in the previous 4 months!

How do we do these tests?
Check out my
blog for FWEC and my video for the Tapeworm Saliva Test.  The FWEC are carried out on a sample of dung which you send off for analysis.  It is really simple but make sure you label the sample and fill in your details!

What if our FWEC are constantly so low we don't need to worm?
You will still need to worm for Encysted Small Redworms and Bots and use a Tapeworm saliva test.

How do we know what to worm for?
The tests will give you results of worm eggs seen in the sample you send.  This will probably show for Stronglye Eggs, Ascarids and perhaps Tapeworm Eggs.  You will then need to worm if the result is Moderate (200 - 1200epg) or High (over 1200epg).  My tests come back as <50epg no eggs in sample.  So I don't need to worm.  Most FWEC companies will advise you if you ask!

How do I accurately worm my horse?
Worm each horse based on their FWEC do not dose all horses the same (as we used to be advised to do)!  You should worm based on the weight of your horse - use a weigh tape, bridge or weigh tables to discover a reasonably accurate weight.
Suggested Routine
End February - FWEC
March - Tapeworm Test
End April - FWEC
End June - FWEC
End August -FWEC
September - Tapeworm Test
December - Worm for Encysted Small Redworm and Bots.

We are strongly advised to poo pick paddocks as often as possible.  Realistically for most of us daily is not feasable, so if you can try to do this once a week at least, keep the pasture clean and many of the worms will be removed too. 

Dung Beetles
This is something I have been thinking about in the last few weeks as I have recently discovered we have dung beetles in our field.  The field where I used to keep the horses had dung beetles, but this is the first time I have seen them since moving the horses 5 years ago.  Basically they are little beetles that you can see moving about in the dung if you remove the top layer.

Dung beetles feed on the juices in dung (I know it sounds disgusting), they bury it underground and when doing  this they take the infective stages of gut parasites (worms) and fly larvae with them - they die.  Also, as I mentioned last week the parasitic worm larvae need damp conditions to move out of the dung.  When the dung beetles remove the juices they disperse the dung too and this leaves an unfavourable environment for the worm larvae too - they die!   So this suggests that dung beetles are good for helping to control parasitic worms.  

However, some chemicals in wormers make the dung toxic which will kill the beetles, ivermectin is one of these, but moxidectin seems to be non-toxic.  Dung beetles also like fresh dung (under 48 hours) so it is best not to remove the new piles.  You can see where they have been because they leave the dung totally dried out and spread!  This means poo picking the older dung and leaving the newest piles until the beetles have finished.

I don't think there has been much research into the use of dung beetles to control worms, but any help from nature is always welcome.

Key Points

  • FWEC  all new arrivals before mixing them with the other horses and keep stabled/separate for 48 hours 
  • Know the weight of your horse and ensure it gets the correct dose 
  • Keep an accurate record of when you worm and/or FWEC your horse 
  • Do not re-feed hay that has been dragged through soiled bedding 
  • Keep all feeding utensils and water containers clean 
  • Stable walls and floors should be scrubbed regularly 
  • All grazing and bedding to which horses have access become infected by worm eggs or immature worms. 
  • Rest each rotation paddock for at least 3 months 
  • Droppings should be collected weekly 
  • Mow patches of coarse grass and herbage which the grazing horses use as lavatory areas as moisture is essential for the development of the free living stages and for the larvae to move out of the dung 
  • Horses should not be allowed access to muck heaps 
  • Horse manure should not be used to ‘fertilise’ horse paddocks

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Until next time!

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