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EQUINE Health
60 www.EliteEquestrianMagazine.com
By Eleanor Blazer
THE WAY OF HORSES
Copyright @ 2018
Controlling roundworms (Parascaris spp./ascarids)
has been an on-going challenge for horse breeders.
The 1916 United States Department of Agriculture book
“Diseases of the Horse” describes how the roundworm affects
the growth and health of horses – unthriiness, diarrhea or
conspaon, colic and respiratory problems. Recommended
treatment compounds were tartar emec, turpenne or
carbon bisulphid for the removal of the parasite. Foals were
treated with a mixture of the chemical of choice and honey
which was placed on the back of the tongue twice a week.
Older horses were fasted for 18 hours and then administered
the poison with a stomach tube. The toxic chemicals basically
caused severe diarrhea and purged the intesnal tract. The
book warns that the treatments are dangerous to the horse
and can cause death or permanent injury to the kidneys or
other organs.
The newborn foal is free from parasites, but it doesn’t take
long for the youngster to be exposed.
Ascarid eggs can live for years in pastures and turnouts on
plants, buckets, fences and stall walls – just waing for the
exploring foal to find and swallow. The eggs can also become
stuck to the mare’s udder and swallowed when the foal
nurses.
The eggs travel to the small intesne where they hatch. After
hatching, the larvae work through the intesnal wall into
the blood stream, reaching the liver and eventually ending up
in the lungs. The larvae are coughed up, swallowed and return
to the small intesne where they complete their lifecycle
- maturing into adult egg-laying worms. The new eggs are
passed out of the horse in the manure where they wait to be
ingested by the next horse. It is esmated the eggs can live
for close to 10 years in a suitable environment. Extreme heat
and cold does not effecvely kill the eggs, which are encased
in a hard protecve capsule.
As the 1916 book stated roundworms can cause poor
growth, coughing, nasal discharge, inflammaon and colic.
But foal owners must realize that youngsters without symptoms
will sll have roundworms. Total eradicaon of roundworms
in the environment is impossible.
Over last 100 years our choice of chemicals and administra
on has improved but the effecveness of our modern
dewormers is decreasing.
A study done in September 2002 on a farm in Ontario,
Canada showed that foals which had been regularly dewormed
with ivermecn since birth had poor roundworm
control – they were resistant to ivermecn. Patrick D Hearn,
F & Peregrine, Andrew. (2003). Idenficaon of foals infected
with Parascaris equorum apparently resistant to ivermecn.
Journal of the American Veterinary Medical Associaon. 223.
482-5, 455. 10.2460/javma.2003.223.482.
To prevent resistance to dewormers the American Associa
on of Equine Praconeers recommends for foals and
weanlings: “During the first year of life foals should receive
a minimum of four anthelminc treatments. First deworming
should be carried out at about 2-3 months of age, and
a benzimidazole drug is recommended to ensure efficacy
against ascarids. Second deworming is recommended just
before weaning (approximately 4-6 months of age). An extra
treatment can be jusfied before weaning if the me period
between the two treatments exceeds 3 months. At weaning a
fecal egg count is recommended to determine whether worm
burdens are primarily strongyles or ascarids, to facilitate the
right choice of drug class. Third and fourth treatments should
be considered at about 9 and 12 months of age, respecvely,
and treatment should primarily be targeng strongyles. Tapeworm
treatment should be included in the 9-month treatment.”
hps://aaep.org/sites/default/files/Guidelines/AAEPParasiteControlGuidelines_
0.pdf
Dewormers are ineffecve on roundworms unl the parasites
become adults, so deworming foals before the age of 2
months is not advised. Deworming foals at an early age sets
up resistance – resulng in dewormers being ineffecve later
when they can be of use.
Care must be taken when administering the first dose of
dewormer. If the foal has a large worm burden the sudden
die-off of adult worms can cause a blockage, resulng in
impacon colic. It should be done under the supervision of a
veterinarian.
By the me the young horse is two years old resistance to
roundworms has developed. Occasionally adult horses will
have a low roundworm burden.
In 1916 managing manure was the key to keeping the
exposure down. The book recommended stalls and pastures
be cleaned daily and the manure not spread on paddocks
where mares and foals were kept. Feed was to be offered off
the ground.
This is true today - management is key. Overstocking pastures
and turnout areas should be avoided. Isolaon of new
horses with dubious health history should be implemented
unl a fecal count can be taken and treatment completed
before introducon to the herd. Manure removal and pasture
rotaon can also help in managing internal parasites.
It is impossible to totally remove the risk of exposure to
roundworms, but it can be decreased.
Roundworms are primarily
a young horse’s nemesis.
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