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Foals:
Getting a head start against worms!
by Helen Barnes BSc, DMM, DipM,
MCIM, Equine Business Unit Manager, Fort Dodge Animal
Health
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The
birth and development of a foal is a memorable
occasion, an occasion that should however be memorable
for all the right reasons.
A
live healthy foal requires considerable time,
money and effort: an area of particular importance
is that of worm control especially as foals have
low resistance to parasites and can quickly acquire
massive worm burdens that can be potentially fatal.
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It
is therefore important to ensure that a foal is born
into an environment that is as parasite free as possible.
The primary source of infection is the mare!
Caring for
the pregnant mare.
During late pregnancy the mare's natural resistance
to worms is reduced, resulting in a rise in the number
of eggs in its faeces; therefore the mare becomes a
significant source of pasture contamination. To help
reduce this contamination as well as to help keep the
mare healthy both during and after pregnancy, it is
important to routinely worm using a product that is
licensed for use in pregnant and lactating mares, such
as EQUEST. In addition the mare should also be wormed
just before foaling, because four or five days after
birth, worms often pass through the mare's milk to the
foal.
Worms
of particular threat to foals.
With no protective antibodies acquired during gestation,
the foal's low resistance to parasites means that it
is particularly susceptible to infection. Two species
of parasite of particular concern are the intestinal
threadworm and large roundworm, species of parasites
to which horses will develop natural immunity.
Intestinal
threadworms:
Infecting the foals soon after birth, usually via the
mare's milk, these small worms - up to 1cm in length,
live in the small intestine of the foal. Because the
lifecycle of this parasite is very short, foals as young
as four weeks of age can develop heavy worm infestations
causing diarrhoea, loss of appetite and dullness. However,
natural immunity is acquired at around 6 months of age.
Large roundworms (Ascarids):
Practically indestructible, the eggs of the large roundworm
that contain the infective larvae are surrounded by
a thick sticky outer coat. No matter how clean the stables
are kept, these parasites eggs will be present. These
eggs can survive for years on buckets, walls, bedding
and pasture and even on the mare's udder. The main source
of infection is eggs in manure: all foals eat fresh
manure every few hours in order to "seed" their digestive
tract with beneficial microoganisms essential for the
proper digestion of vegetable matter. Infected by ingesting
these eggs, the larvae of this parasite migrate through
the foal's bloodstream to its liver and lungs, causing
coughing, fever and loss of appetite, before they return
to the small intestine. In the small intestine they
develop into adults. These adults reach up to 40 cm
in length, and can be present in the foal's small intestine
from 12 weeks of age. Heavy burdens of these adult worms
causes weight loss and can in rare cases result in a
rupture of the gut. Natural immunity is acquired at
around 18-months of age.
Damage
inflicted to the foal by parasites may be gradual and
subtle, with no noticeable signs from the onset. However,
the foals growth and development will become impaired,
its performance ability reduced, and its resistance
to disease lowered - resulting in potential complications
longer term. To protect the foal and give it a head
start worming is vital.
Worming
foals.
The worming of foals should start at four to six weeks
of age or as soon as they start to graze on pastures;
with treatment being repeated every four weeks until
six months old. Thereafter routine worming can be continued
as per wormers' recommended dosing interval, i.e. every
13 weeks with EQUEST. With regard to tapeworm, infestation
is unlikely to occur in foals under 2 months of age,
so treatment of foals below this age is not considered
necessary. Tapeworm is controlled by means of a double
dose of a pyrantel-based wormer or with a single dose
of a praziquantel-based wormer (i.e. EQUITAPE).
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When choosing a wormer
for a foal it is important to avoid drugs not licensed
for use in very young foals, i.e. EQUEST should
not be given to foals younger than four months of
age. |
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Dose the foal according
to its body weight, as under dosing results in more
worms surviving leading to pasture contamination,
as well as contributing to the development of resistance,
and overdosing can cause undesirable side effects.
As the foal is developing its weight will be constantly
changing, therefore, foals should be weighed prior
to each treatment either by means of a weigh tape
or ideally weigh scales. |
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· Ideally foals should
not be grazed alongside older horses as foals are
a major source of pasture contamination and require
more regular worming. |
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A paddock rotation
system should be adopted so that nursing mares and
their foals do not graze the same area in successive
years. Ideally rotate land with sheep or cattle,
as worms that affect horses are host specific and
cannot survive in sheep or cattle, as such any larvae
they eat will be destroyed. |
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· Avoid turning out
young stock onto small turn out paddocks as pasture
will develop extremely high larval counts particularly
if droppings are not removed each day. |
By
adopting a rigorous worming programme, supported by
pasture management, the risk of parasite damage to the
foal can be reduced, thereby giving the foal a head
start so that it develops into a beautiful, healthy
horse.
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