Intestinal Parasites in Sheep and Goats - OSU

Internal Parasites in Sheep and Goats
E M 9055 • Feb ruar y 2013
A. Villarroel

What parasites are commonly found in
sheep and goats?

How do parasites cause disease?
Most of the damage caused by parasites is due to
mechanical irritation of the tissues they affect and
the obstruction of an organ when there are too many
worms.

Parasites commonly found in sheep and goats
can be divided into two general categories: external
(skin) and internal (organ) parasites. Because internal
parasites tend to prefer a specific organ, there are
multiple types. The most common internal parasites in
sheep and goats are: lung worms (Dictyocaulus spp. or
Muellerius capillaris); stomach worms (Haemonchus
contortus, commonly called barber pole worm); liver
flukes (Fasciola hepatica); and intestinal parasites,
the most common of which are coccidia (Eimeria or
Isospora).

Lung worms
Lung worms irritate the bronchioles inside the lung
and cause a local reaction with mucus and white blood
cells (phlegm) that are trying to get rid of the parasites.
The irritation and pain causes the animal to cough.

Stomach worms
Stomach worms are voracious bloodsuckers and
will destroy the lining of the stomach to access the
bloodstream. The destruction of the lining of the
stomach can cause colic (abdominal pain), diarrhea,
anemia, and weight loss due to the animal’s inability to
digest feed completely.

How do sheep and goats get infested
with parasites?
When animals “get” parasites, we refer to it as an
infestation and not an infection, which is caused by
bacteria and viruses.
Parasites grow and reproduce in certain
environments. Sheep and goats that live in those
environments are at high risk of becoming infested.

Liver flukes
Liver flukes burrow tunnels in the liver, causing
scarring as the body tries to repair the damage. Because
scar tissue is not functional, the liver loses part of its
normal function, which includes filtering the blood of
toxins and waste products. The accumulation of these
toxins in the animal’s blood can severely damage other
organs, including the brain. Therefore, a common sign
of liver fluke infestation is depression or stupor.

• Lung worms and liver flukes grow and reproduce
inside snails, which live in stagnant water. Sheep
and goats that have access to stagnant water are
at risk of being infested by these parasites.
• The eggs and larvae of stomach worms are commonly found on wet vegetation, like dewy grass.
Larvae can move up the grass where they are
eaten by sheep or goats.
• Coccidia mostly affect young animals because
they have not yet developed their immune
defenses. Coccidia commonly live on the ground
but are usually not a problem unless there is
overcrowding of animals.

Coccidia
Coccidia live in the lining of the intestines and
destroy the crypts that the animals need to absorb
nutrients. Therefore, the most common sign of
coccidian infestation is diarrhea (detected by dirty hind
ends), and failure to thrive or weight loss.
Aurora Villarroel, DVM, MPVM, PhD, ACVPM, CVA; Extension
veterinarian, Oregon State University.

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What are typical signs of parasitism?
• Weight loss—Animals don’t get all the nutrients
they need.
• Diarrhea—Detected by dirty tail and hind end
(Figure 1).
• Rough hair coat—When nutrients are insufficient, the animals’ hair loses its luster.
• Depression—Animals keep their head and ears
down and are not willing to stand for long
periods of time.
• Weakness—Animals are easier to catch or
unstable when walking.
• Anemia—Animals’ gums, perineum, and eyes
appear white due to blood loss (Figure 2 and
Figure 3).
• Fever or, in the late stages of disease, cold
extremities (e.g., ears and legs).
• Fast breathing (lung worms)—Animals try to
get oxygen into their damaged lungs.
• Coughing (lung worms)—Animals cough from
the irritation of their damaged lungs.
• Bottle jaw (stomach worms and liver flukes)—
Animals have fluctuant swelling under the jaw
from the accumulation of fluid (submandibular
edema). Sometimes it can spread to under the
abdomen.

Figure 1. Evidence of diarrhea on a goat: dirty
hind end.

from 3 to 5 animals and place them into a ziplock
bag. Make sure to mix the pellets well.
• Testing individual animals is more specific
because you can establish the parasite burden in
each animal and the effect of the treatment. After
treating individual animals, separate them from
those that are not treated.

How to test for parasites?

Procedure: Take approximately 20 fecal pellets
from each animal and place them in individual
ziplock bags identified with the animal’s name or
ID number.

The standard method to test for parasites is to look
under the microscope for parasite eggs in the feces
of the animals—even for lung worms. When animals
cough up lung worms, they will sometimes swallow
some of the worms, which then enter the intestinal tract
and lay eggs. Thus, lung worm eggs can also be found
in feces. The various parasite families have different
egg shapes, which helps in identifying them. However,
to determine the specific parasite, other tests may be
needed.

Work with your veterinarian to establish the most
appropriate testing strategy for your premises. As a
general recommendation, if it is the first time you are
testing your herd, it is best to perform a group test
to see if parasites are an issue on your premises. It is
generally suggested to test each pen as a separate group,
even if it is your first time testing your herd. Individual
testing is best used to identify potential carriers or high
shedders to target for possible culling.

Testing strategies:
• Group testing is less expensive but less specific.
If the sample is positive for parasites, it will not
be possible to know which animals are infested
and which are not, and therefore all animals in
the group will have to be treated.

When to treat parasitism?
Treatment recommendations have changed over the
years. The current recommendation is to treat only
when necessary and only the animals that need it.
This implies the need for testing (as explained above).

Procedure: Take approximately 10 fecal pellets

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Common times to test include before lambing/kidding
and at weaning.

Table 1. Commonly used limits to establish
treatment against parasites

Finding parasite eggs under the microscope does not
necessarily warrant treatment of infested animals. For
example, lung worms and liver flukes should be treated
any time eggs are found, but for stomach worms and
coccidia, it is recommended to only treat when high
burdens are observed (see Table 1). The reason for this
is that treating low burdens of stomach worms and
coccidia can increase the chance of parasites developing
drug resistance. Having susceptible worms in the
environment helps control the population of resistant
parasites because they mate with susceptible worms.

Liver flukes

any number of eggs found in feces

Lung worms

any number of eggs found in feces

Barber pole worms

>500 eggs/g feces

Coccidia

>1,000 oocysts/g feces

Food and Drug Administration and have a specified
withdrawal time for meat and milk (if applicable, for
dairy sheep and goats). Using a drug in any way other
than that listed in the drug pamphlet is considered
extralabel drug use and can only be done by veterinary
prescription.

For stomach worms (Haemonchus contortus,
commonly called barber pole worm), a simple visual
inspection of the eyes can determine if animals are
infested with a high burden of parasites. Animals
that are losing a lot of blood due to the bloodsucking
parasites show pale mucosae in some areas of the body
such as the gums (Figure 2), the perineum (Figure
3), and under the eyelids. Sheep and goats should
have pink mucosae. If these tissues are pale, it is likely
because of blood loss. Colored charts are available on
the Internet to categorize the color of the inside of the
eyelids using the FAMACHA© system.

Table 2 lists the dewormers currently approved
for use in sheep and goats and the parasites they are
effective against. It is very important to notice that all
dewormers are not effective against all parasites. In
addition, some dewormers that used to be effective
against a specific parasite are no longer effective, due
to the development of resistance in some worms.
Therefore, just because you apply a dewormer doesn’t
mean you’ve killed the worms; you have to be sure
to use the right dewormer for your specific situation.
Sheep and goats have a much higher metabolism rate
than cattle. Therefore, drug dosages will likely be higher
than those listed for cattle.

How to treat parasitism?
There are only a few drugs approved to treat
parasites in sheep and goats. According to the Animal
Medicinal Drug Use Clarification Act (AMDUCA), all
drugs used in food-animals need to be approved by the

Treatment should be adjusted to the worm burden.
When the burden is very high, killing all parasites at

Figure 2. Comparison of the gums of a normal sheep (left) and a sheep with severe
anemia due to a high burden of stomach worms (right).

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Figure 3. Pale perineum in a sheep
with severe anemia due to a high
burden of stomach worms. A white
gauze is shown for color comparison.

Table 2. Current drugs approved for use in sheep and goats.
Active ingredient

Liver flukes

Lung worms

Barber pole worms

Coccidia

Albendazole

X

X

X

-

Ivermectin

-

X

X

-

Levamisole

-

X

X

-

Moxidectin

-

-

X

-

Lasalocid

-

-

-

X

Decoquinate

-

-

-

X

once can create more problems, such as plugging the
digestive tract with dead worms. In these cases, it may
be preferable to treat with lower doses at frequent
intervals. Consult with your veterinarian about the best
option for your specific circumstances. As indicated
above, most of these treatments will require veterinary
prescription.

flock. These animals should be culled from the flock
to decrease the burden of parasites in the entire flock
and to increase the susceptibility of parasites in the
flock to dewormers. This action can prevent animals’
reinfestation and need for treatment.
Treatment of parasitism should include eliminating
risk factors that will contribute to future reinfestation,
as well as selecting animals that are resistant to parasite
infestation.

Some dewormers can be given orally or be
injected subcutaneously (under the skin). Generally
speaking, injected dewormers intended for treating
gastrointestinal parasites take longer to take effect than
oral medications and last longer at low concentrations.
This long action at low concentrations is considered
to induce resistance. However, given your specific
circumstances, your animals may respond better to
injectable rather than oral dewormers.

How to prevent parasitism?
The best prevention is to reduce your animals’
exposure to parasites by providing a clean
environment—beginning at birth—and avoiding
overcrowding of pens or premises. Balanced nutrition is
very important to keep animals healthy and help them
develop appropriate resistance to external pathogens,
especially for dams before and after lambing/kidding.

Affected animals should be separated from
unaffected animals at the time of treatment. Treated
animals should be moved into an area that can be easily
cleaned and disinfected.

Other important preventive actions are to:
• Avoid pasturing in damp areas and during early
morning and evening hours, when there is dew
on the pasture.
• Rotate pastures to avoid high burdens of
parasites.
• Select animals from bloodlines that show low
worm burdens.

After treating affected animals, wait 3 to 4 weeks and
retest to determine the effectiveness of the treatment.
Animals that still have high burdens after treatment
should be retreated and then retested 3 to 4 weeks later.
Animals that still have high burdens after a second
treatment are likely to be very susceptible and can act
as carriers for parasites, infecting other animals in the

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Published February 2013.

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