do these three conditions have in common? Colic and Peritonitis are
serious conditions that require immediate veterinary treatment, and
both can be caused by worms!
This is something I discovered recently when my 6yo Arabian stallion
Finn, suffered a colic episode that also resulted in hypothermia as
he went down on a cold wet day. Thankfully, I went to his paddock again
at lunchtime (the boys had been fed at around 9am) to get the float
for re-filling with hay, and found him laying down in the rain. When
I got closer, I saw he was in a lot of pain so immediately gave him
some rescue remedy (always carry some in the car) then raced back home
for a warm rug, the Equine Colic Relief (ECR) and the stethoscope.
After administering the ECR I waited the 45 minutes suggested to see
if his condition would improve. In that time, I took his heart rate
which was up to 48bpm and allowed him to lay down as he was quiet and
not wanting to roll. His 3 paddock mates all stood around us looking
concerned, with the most senior gelding occasionally trying to chew
on Finn to get him up.
When there was no noticeable difference in his pain levels, gut sounds
or heart rate after the 45 mins I called the vet who arrived within
After checking all his vital signs he administered some painkillers
and muscle relaxant then did a rectal exam which confirmed an impaction,
so Finn was then stomach tubed with Parrafin and Tympanel to help the
I was very proud that he handled his first rectal exam and stomach tube
without even a twitch!
Finn then seemed much better (the drugs were working) so I walked him
home on the vet’s advice as movement would help the impaction
shift, and with his mates following, he strode home and happily tucked
into some hay in the barn and yard overnight.
The next morning though he was quite depressed again and not eating
and after I’d fed all the others, he was laying down again obviously
in pain. Another visit from the vet confirmed a high temperature indicating
an infection so he was treated aggressively with antibiotics for peritonitis.
He seemed to improve the next day so was moved to fresh pasture, but
by the following day he was down again. This time the vet suggested
worming him again (he’d been wormed 10 days prior with Panacur)
with Equest Plus for tapeworm as they have been known to cause an impaction
So we did that immediately and gave more painkillers to keep him comfortable.
The next morning he was fine and his manure was already passing a large
amount of tiny hair like worms which I believe were small strongyles.
After passing that burden, he made a complete recovery thankfully -
many horses get seriously ill or die if not treated correctly.
Finn may be one of the 20% of horses that carry 80% of the worms so
it's possible he had a large number of encysted stongyles that upon
worming with a single dose of Panacur, emerged to take the place of
the cleaned out worm population. This mass emergence would have caused
both peritonitis and the impaction colic.
My intention had been
to worm him with Panacur for 5 days in a row to kill any encysted strongyles,
but I couldn’t get the horses to take it in their feed and dosing
four strong and protesting boys with the drench gun every day for 5
days (with limited success on my own – liquid wormers are very
easy to spit out), I gave up and decided to just use Equest next time
they were due.
And that was my mistake
as it had been exactly 12 months since they were wormed with Equest
so they were overdue. I’ve since realised I should have been worming
twice yearly with Equest for encysted strongyles (Dr Ann Nylands book
& Donkey Worms & Worming ) gives good schedules to follow.
So what are encysted strongyles?
They are a 3rd stage larvae of the small strongyle (cyathostomes) that
are eaten and go into the lining of the horse’s colon and form
a cyst. This is why they are called encysted strongyles and the only
chemicals that will kill them are moxidectin with a 90% success rate
(in Equest/Quest wormer) and Fenbendazole in Panacur 100 if it’s
used for 5 consecutive days at 10ml per 100kg. No other wormer will
be able to kill them.
Encysted stronglyes can stay in a horse for years (or as little as 8
weeks) before they develop into 4th stage larvae and enter the colon.
If there’s a huge
amount of them, the emerging may kill a horse and I suspect many ‘mystery’
deaths could be attributed to them. If there are less but a lot emerging,
the horse may get colic, and/or scour and/or get edema.
So it’s vital to
worm your horse at least twice yearly with Equest/Quest or Panacur (if
you can get them to take it effectively) to ensure that the emerging
encysted strongyles won’t harm your horse.
Also useful to know is that worm counts will not show how infested a
horse is with encysted strongyles!
There is a lot more in depth info on this in Ann Nylands book which
I highly recommend to every horse owner. To sum it up I quote from the
book ‘Research has shown that cyathostomes (small strongyles)
have become more and more important as a cause of sickness and death
in horses, and today are considered the main reason for worming horses.
If you want to save yourself from a
huge vet bill, and your horse from all those injections – don’t
put it off! Equest is available (often at discount prices) in many
online stores and is sold by most saddlery stores/vets.
Why I Use
I would love to be able to worm my horses
more naturally, and years ago I tried it that way, but their health
was suffering due to the following issues I have with the place I
• Too small for the number of horses (15 on less than 40 acres).
• Not enough slaves to pick up poo all the time and land too
steep for poo vacuum cleaners!
• Not enough paddocks to rotate around to let them rest for
• Neighbours who don't worm their horses for bots and so my
horses get infected too.
• A wet climate which allows worms to spread easily (they travel
in water and along grass that is covered in water droplets).
• Breeding young horses who are more susceptible to worm infestation
so they need treatment more regularly until around 3 yrs.
• Natural wormers don't really work as my faecal egg counts
• Previous problems with colic symptoms in various horses which
I couldn't attribute to anything else.
Since reading Ann Nylands book I've come to realise that perhaps the
only way you can get around using less chemical wormers is to have
the opposite of all the situations I listed above, and/or use a long
acting wormer like Equest.
Also, some horses are more likely to
have a better immunity to worms so if you only had a couple of horses
who lived together on a largish acreage then you might get away with
worming naturally and keeping a check on their egg counts.
However, egg counts won't tell you if they have tapeworms or encysted
strongyles that can stay in the gut wall for years, just waiting for
the right conditions to hatch.
From a total of 280 votes – it
looks like less than half the voters in a recent online poll knew
what to treat encysted strongyles with (Moxidectin or Fenbendazole).
Results of the Poll by The Horse.com
Which of the following dewormers do you use to treat encysted small
• Ivermectin: 35.57% (164)
• Moxidectin (e.g., Quest): 25.60% (118)
• Pyrantel Pamoate (e.g., Strongid): 19.09% (88)
• Fenbendazole (e.g., Panacur): 15.84% (73)
• Other: 3.90% (18)
Ivermectin will not touch encysted
strongyles and there seems to be more branmds of wormer these days
that contain Ivermectin (+ other chemicals) than there are alternatives.
To better understand worming and for a complete list of wormer brands
with their chemical compounds, get
Dr Ann Nylands book here.