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Parasites & Deworming



There are many different parasites that infect our sheep and goats here in Pennsylvania and Maryland.  Weight loss, decreased weight gain, and illness can result in production loss on your farm.  With increased resistance to our current dewormers, correct management of the animals and appropriate use of the dewormers will allow your farm to be successful at winning the war against parasites.

What Parasites are Affecting My Animals?

Why are parasites so difficult to control in our sheep and goats?

What is parasite Resistance?

How to slow parasite resistance on your farm.

Other methods to Control Parasites on your farm.


There are over 15 internal parasites that affect our sheep and goats.  We will focus on the 5 most commonly encountered parasites.

  • Haemonchous species – "The Barber Pole Worm."
    • Clinical Signs:
      • Blood loss (anemia)
      • Bottle jaw (low protein in the blood)
      • Rough hair coat
      • Weakness
      • Sudden death.
    • Likes to grow in warm, wet environments.
  • Ostertagia species –  "The Brown Worm," "Telodorsagia."
    • Clinical Signs:
      • Loss of appetite
      • Diarrhea
      • Weight loss
    • Likes to grow in cool, moist environments, and is commonly seen in the fall.
  • Trichostrongylus species – "The Bankrupt Worm."
    • Clinical Signs:
      • Loss of appetite
      • Diarrhea
      • Weight loss
      • Wasting.
    • It likes to grow in warm, moist environments.
  • Moniezia species –The Common Tapeworm.
    • Resides in the small intestine.
    • Clinical Signs:
      • Poor growth.
      • Weight loss.
      • Can predispose to other parasite problems.
  • Coccidia (not an intestinal "worm").
    • Ingested in feed, water, and contaminated environment.
    • Stress and lack of sanitation are the major causes of infection.
    • Clinical Signs:
      • May or may not see diarrhea with infection.
      • Poor Growth.
      • Weight loss, chronic scarring of intestines – leading to poor nutrient absorption.


  • Sheep and goats housed on pastures will graze close to the ground, where higher levels of parasite eggs exist.
  • Over-population of animals on pastures leads to extensive parasite loads on the pastures.
  • Feeding grain and hay  on the ground allow the animals to ingest parasite eggs.  (This is a major cause of coccidiosis).
  • The temperature and humidity of the Northeast provides optimal growth conditions for parasites.
  • The parasites have adapted to survive severe environmental stresses.
  • Over-use and inappropriate use of parasite dewormers have led to parasite resistance to our current medications on the market.
  • Coccidia is not controlled by the use of dewormers; but rather requires the use of coccidiostatic or coccidiocidal drugs.


  • Resistance is the ability of the parasite to survive when dewormers are administered to the animal host.
  • This means that the dewormer is either not effective or only partially effective at killing worms and curing clinical symptoms of the disease.
  • As worms develop strategies to survive against a particular dewormer, they pass that strategy to its offspring (in other words, resistance is heritable).
  • The main cause of resistance is frequent deworming, such as:
    • Deworming all the animals in the herd without regard to how heavy the parasite infection is.
    • Deworming based on the calendar.


  • Use Dewormers at the appropriate dosage.
  • Strategically monitor the animals in your herd and treat those that need treatment.  Monitor:
    • Eyelid color – Anemia (pale eyelids) can be caused by coccidia and Haemonchus.
    • Body weight – Run your hand along the animal's back to determine body condition.  Thin animals may be struggling with parasite loads.
    • Manure Consistency – Is the manure in small, individual pellets, clumpy (similar to dog stool), soft (like cow manure), or watery and runny (diarrhea).  Heavy parasite loads often, but not always, cause clumpy, soft, or runny manure.
    • Jaw swelling – Is there evidence of bottle jaw?
    • Coat condition – Is the hair/wool unkempt?  Poor nutrition as a result of intestinal parasites can cause poor hair coats.
  • Quarantine new animals, do a fecal egg count, and deworm.  Do not place on pasture or with herd-mates until a low egg count is identified.
  • Genetic selection – 15 percent of your animals will account for 50 percent of the worms.
    • Categorize your animals by litter size (singles, twins, triplets or more).
    • Have Fecal Egg Counts done for all animals in each group.
    • Consider culling animals in each group that repeatedly have the highest egg counts or require more frequent deworming, as these animals have less genetic ability to naturally fight off worms.
    • Have Fecal Egg Counts done on your rams/bucks throughout spring/summer and cull the males with consistently high fecal egg counts.
  • Perform Fecal Egg Count Reduction exams.

Fecal Egg Count Reduction Exam:

  • Helps us determine:
    •   Which dewormers work on your farm.
    •   How contaminated your pastures are.
    •   Resistant animals in your herd/flock.
  • Procedure:
    • Bring us a sample of at least 1 teaspoon of manure from the animal.
    • We will run Fecal Egg Counts and prescribe the appropriate dewormer.
    • Re-run a Fecal Egg Count at appropriate time after dewormer administration.
    • Determine amount of reduction of eggs – Greater than 90 percent reduction will tell us that that dewormer works on your farm.

Other methods to Control Parasites on your farm:

  • Rotating pastures so that each pasture has 6 weeks "off" of animals to allow desiccation of eggs.
  • Baling hay off the pastures that are not currently being grazed can reduce worm load.
  • Mowing the grass in pastures that are not currently being grazed keeps the grass in a vegetative state.
  • Grazing sheep and goats with other species, such as horses or cattle.
  • Provide proper nutrition to the animals.
  • Graze taller pastures.  Do not let the animals eat the pastures down too low.
  • Till soil between grazing seasons.
  • Do not worm every animal in the herd/flock, leaving some refuge parasites.
  • Consider raising animals on dry lot, rather than pastures.



Parasitism involves a complex interaction of host, parasite, and environment.  Regular close examination of your animals combined with Fecal Egg Count Reduction exams, appropriate treatment, and management strategies, we can work together to control parasites and raise healthy and happy sheep and goats.