Parasites of Goats
Bill Pomroy

Internal parasites could easily be ranked as the number one health problem of goats in the Southern United States
Oklahoma has
Mild climate
Beneficial to parasites
Yearly rainfall
Still has a winter
Hot dry summer

Consequence of climate
Good environment for internal parasites to survive on pasture and be available to grazing goats and sheep during most of the year
Goat producers are constantly fighting against internal parasites

Gain Control/ Give the Parasites are “harder time”
Better understanding of the life cycle
Optimum environmental conditions
Recognise the signs of parasitism
Preventive management

Worms of goats
Worms in a group called the trichostrongylids are the most important
Live in the abomasum (true stomach) and small intestine
Sometimes called “hairworms” or “scour worms”

Worms in Goats cont.
Three main species
Haemonchus contortus
“Barbers pole worm”
Sucks blood!!!!!!!!
Ostertagia circumcincta
“Small brown stomach worm”
Lives in mucus layer and feeds on mucus
Trichostrongylus colubriformis
“Bankrupt worm”
Lives in the mucus layer of the small intestine and feeds on mucus

Worms in goats cont
Several minor trichostrongylid species
i. e. cause fewer problems than the big three
Trichostrongylus axei
Nematodirus filicollis and N. spathiger
Trichostrongylus vitrinus and T. capricola
Cooperia curticei

Other types of worms
Generally less problematic
Strongyloides papillosus
Mainly a problem of very young lambs
Bunostomum trigonocephalum
Oesophagostomum venulosum
Trichuris ovis
Whipworm lives in the caecum

Slide 9

"Haemonchus adults in the abomasum"
Haemonchus adults in the abomasum

"All trichostrongylids produce similar eggs..."
All trichostrongylids produce similar eggs which are passed in faeces

"A first stage larvae develops..."
A first stage larvae develops in the egg

"On pasture these L1 feed..."
On pasture these L1 feed on bacteria in faeces and moult to L2 and then to L3
The L3 retains the old cuticle or “skin” of the L2 for extra protection

"Note how the old cuticle..."
Note how the old cuticle is surrounding the L3 stage
This means the L3 can’t feed and must rely on stored metabolites or energy to survive
This is a critical issue for the free-living stages

Conditions for Development of Free-living Stages
They need a food source which is bacteria of which there are plenty in faeces
They need oxygen but that is usually not a problem

Conditions for development cont.
They need a suitable temperature
Minimum is 50F (10C) and maximum is 105F but the optimum is 77F (25C).  Hotter than optimum and few manage to hatch and develop.  The speed of development up to 77F is temp dependent

Conditions for development
Moisture is critical too!
Eggs, L1 and L2 are very susceptible to desiccation
A major advantage with your dry summers
L3 are tougher but still susceptible to desiccation
Especially Haemonchus
Some of the others have been shown to be able to be dried out and then rehydrated again

Conditions for survival and infection
Are somewhat different to those for development
Survive best at about 50F (10C)
As they get warmer they move and use up stored metabolites and energy
When they run out of energy they die
At 50F may live in a fridge for months but on pasture will be shorter

Survival and infection cont.
Summer probably 30-60 days
Winter 120-240 days
Haemonchus probably doesn’t survive your winters too well – too cold, but some of the other types of worms will survive OK

Larvae move randomly on moisture film
They need the surface tension layer
Some move up the grass or plant and are then available to the grazing animal to eat

"L3 larvae caught in a..."
L3 larvae caught in a dew droplet on a stem of grass

Infection cont.
Wet conditions or heavy dews
= larvae are picked up daily
Dry conditions
=larvae are not picked up
Probably of major importance in this region

Infection cont.
Rains following a dry spell may result in some dehydrated larvae becoming available again
Not an apparent problem for Haemonchus

Optimum conditions
Late winter early spring = light infection to seed new larvae onto pasture
Mid to late spring = heavy infection
Summer = too dry for much pick up or survival.  Probably a major limiting factor to break the seasonal cycle
Fall = may be moist enough for some development and subsequent pickup
Winter = too cold for much development

After infection
L3 develop a close association with the host’s gut lining and develop there for at least one further moult

"Abomasum with developing Ostertagia larvae..."
Abomasum with developing Ostertagia larvae within the mucosa

Adults in the gut
Apart from Haemonchus which sucks blood all the rest are “mucus browsers”
They live within the mucus lining of the gut wall and slurp up liquid feed such as mucus and digested food

"Trichostrongylus in cross section in..."
Trichostrongylus in cross section in the mucus layer of the small intestine

Periparturient Rise in Faecal Egg Counts
Around kidding/lambing there is a decline in the host’s immune response
More worms able to establish
Existing worms able to produce more eggs
Fewer worms expelled by the host
Is considered important as a kick start to the new season’s contamination

Hypobiosis or Inhibited Development
A survival mechanism of worms
They ceases development in the host in the early stages soon after infection
Is a mechanism to evade unfavourable environmental conditions for larval development on pasture
When conditions improve they reactivate.
Usually stay inhibited for one season eg. winter
Evade the host’s immune response
All trichostrongylid worms can