Gastrointestinal Round Worm (Barber Pole Worm) – Haemonchus Contortus
The round worm is a blood sucking parasite that can cause severe anemia, protein
loss and death. It causes lower growth rates, reduced reproductive performance and
higher rates of illness and death in the goats in infects. This parasite can consume
up to 10% of an animals total blood volume in a day and easily cause them to quickly
Lifecycle takes approx 21 days to complete
Larvae in L3 stage of development are ingested by goats mainly while grazing in a
pasture, generally grass or hay, where infected goat pellets had been dropped earlier.
The larvae go to the true stomach of the goat.
One of two things can happen then.
The larvae may proceed in developing into further larval stages moving toward becoming
The other option is for the larvae to go into a state called hypobiosis or arrested
development. This is similar to a bear going into hibernation for the winter.. This
situation occurs when the larvae in the stomach determine that conditions may not
be right for it to successfully complete the growth to an adult at that time. This
may occur when the winter is too cold or in the summer when it is too hot and dry
to survive. In arrested development stage they sit quietly in the stomach following
infection and don't become adults until several months later. This is an important
adaptation for keeping the worm around through cold winters when eggs and larvae
don't survive well on pasture. The worms that became arrested in the fall resume
development in the spring and reproduce. When the worm comes out of the arrested
development and resumes growth, massive numbers become mature adults over a short
period of time and the resultant egg production and deposition in the feces can be
very high as well as having severe adverse effects on the animal
For the larvae that do not go into arrested development, they will transform to a
L4 stage into an adult which can be up to ¾ of an inch in size. The signs that indicate
to not go into arrested development can be green grass coming through the system,
an increase in the temperature such as coming out of winter, rainy weather following
a drought period or increased estrogen levels in the goat.
Once they reach the adult stage, in about 14 days the female begins to lay eggs in
the true stomach.. The female can lay up to 5,000 to 10,000 eggs per day. Egg laying
will stop in very hot/dry environments.
The eggs laid in the true stomach are passed out of the body through goat feces (goat
When the environment is right, the eggs in the droppings will hatch into larvae.
The pellet has to be moist, soft and a warm temperature for the eggs to hatch. That
can occur from a rain, a leaking water tank or similar things. Spring is a common
time for this to occur.
After hatching, they move through several stages of development (L1, L2, L3) until
they become the same type of larvae that were eaten earlier that started this life
cycle. This can be as short as 7-10 days of going from egg to L3 larvae. During the
colder months, larvae development on the pasture is delayed and may take up to a
month or two to reach the L3 stage.
The L3 larvae have a protective sheath making them relatively resistant to adverse
environmental conditions and can survive for months.
The L3 larvae climb up on blades of grass and wait to be taken in by your goats
so that starts the life cycle all over again.
The L3 larvae can live in the pasture for up to 90 days in the summer and 180 days
in the fall/winter. They love an environment where the temperature is between 70-80
degrees and there is an average of 2 inches of rain a month. . But at very high temperatures,
larvae may only survive for 30 days.
The larvae can live in temperatures below freezing, but may die off during hard freezes.
Moisture is crucial for development and survival. Because the initial development
and survival occurs within the feces, moisture is usually adequate to complete development
to the L3 larvae, however if the feces dries out quickly, due to high temperatures
and/or physical disruption, the L1/L2 stage larvae are susceptible to desiccation
and will die. If feces remain intact, retain some moisture and do not get too hot
or too cold, the L3 larvae may remain alive for months.
Sustained temperatures above 95% are usually lethal.
The moisture conditions at ground level under forage cover usually is adequate for
larvae to move around and survive.
Since the larvae don’t feed, their length of survival depends on how fast they use
up their energy reserves. So the hotter it is, the faster they move and use up energy
stores and survival is shorter.
Eventually, larvae move up and down the forage when there is moisture medium such
as dew or rain. For the most part, larvae do not move past 12-24 inches from feces
or 2-4 inches up the forage
As long as the temperature and moisture conditions remain warm and wet, development
and survival continues and pasture contamination accumulates. If the temperature
gets too hot/cold and/or the moisture conditions become dry, development and survival
are threatened and pasture contamination dissipates.