Haemonchus contortus, commonly known as the barber’s pole worm, is an internal parasite affecting goats and other small ruminants across the globe. This blood-feeding nematode resides in the abomasum, or true stomach, of its host, where it can cause severe health issues and economic losses for producers. The parasite thrives in regions with warm, moist climates that favor its life cycle, but it is increasingly found in more temperate zones. Its high reproductive rate and the growing problem of resistance to common dewormers make it a challenge for goat health management.
The Haemonchus Contortus Life Cycle
The life cycle of Haemonchus contortus is direct, meaning it requires only one host to complete its development. Adult female worms in the goat’s abomasum are capable of laying between 5,000 and 10,000 eggs per day. These eggs are passed out of the goat in its fecal pellets and onto the pasture. In the environment, the eggs hatch and develop through larval stages.
Under optimal conditions of warmth and humidity, these larvae develop into the infective third-stage (L3) in as little as three to four days. The L3 larvae migrate out of the feces and onto blades of grass, moving with the morning dew, where they wait to be ingested by a grazing goat. Once consumed, the larvae travel to the abomasum and mature into adults, completing a cycle that can take 17 to 21 days. An adaptation is hypobiosis, a state of arrested development where larvae can overwinter inside the host, emerging in the spring.
Signs of Haemonchus Contortus Infestation in Goats
The clinical signs of a H. contortus infestation, known as haemonchosis, are primarily caused by blood loss. Adult worms use a small, tooth-like structure to pierce the lining of the abomasum and feed on the host’s blood. A goat with a burden of 5,000 worms can lose up to 250ml of blood each day, leading to anemia. This anemia is most visibly indicated by pale mucous membranes in the lower eyelid.
As the blood loss continues, goats may develop edema, which is a swelling caused by fluid accumulation. This is commonly seen under the jaw and is referred to as “bottle jaw.” Other signs include a failure to thrive, weight loss, weakness, and lethargy. Unlike many other gastrointestinal parasites, diarrhea is not a common sign of a pure H. contortus infection. In severe cases, especially in young or weak animals, sudden death can occur before other signs are noticed.
Diagnosing Haemonchus Contortus
Diagnosing haemonchosis relies on a combination of observing clinical signs and using specific diagnostic tools. The FAMACHA system is a practical on-farm method for assessing anemia. This system uses a color-coded chart to score the mucous membranes of the lower eyelid on a scale from 1 (red, healthy) to 5 (white, severely anemic), allowing producers to identify which animals require treatment. A score of 3 or higher often indicates a need for intervention.
Another diagnostic tool is the Fecal Egg Count (FEC), which quantifies the number of worm eggs per gram of feces. While FECs are useful for monitoring pasture contamination and testing dewormer effectiveness, they are not always a direct indicator of the number of adult worms an animal is carrying. FECs are best used in conjunction with clinical signs and FAMACHA scores to make informed management decisions. Post-mortem examination of a deceased animal provides a definitive diagnosis by revealing the worms in the abomasum.
Treatment Options for Infected Goats
The primary treatment for haemonchosis involves the use of anthelmintics, or dewormers. These drugs are grouped into classes, such as benzimidazoles, macrocyclic lactones, and imidazothiazoles. A challenge in controlling H. contortus is the widespread development of anthelmintic resistance. The parasite’s rapid life cycle and high reproductive rate contribute to its ability to quickly develop resistance to drugs that are used too frequently.
Due to this resistance, treating the entire herd at once is no longer recommended. Instead, a strategy called Targeted Selective Treatment (TST) is advised. This approach uses diagnostic indicators like FAMACHA scores to identify and treat only the animals that are clinically affected. This leaves a portion of the parasite population in “refugia” (untreated animals), which helps to dilute resistant genes and preserve dewormer effectiveness. For severely anemic goats, supportive care, including nutritional support and blood transfusions, may be necessary.
Preventing Haemonchus Contortus Infestations
Long-term prevention is centered on management practices that disrupt the parasite’s life cycle and enhance the goat’s natural ability to resist infection. Effective strategies include:
- Implementing rotational grazing systems that move goats to fresh pasture before they graze too low, reducing parasite intake.
- Allowing pastures to rest to decrease the larval population, as larvae die off over time, especially in hot, dry conditions.
- Co-grazing or alternating pastures with other species like cattle or horses, which act as dead-end hosts for H. contortus.
- Providing proper nutrition, particularly adequate protein, to bolster a goat’s immune system and make it more resilient to infection.
- Selectively breeding for animals that consistently show lower fecal egg counts or better resilience to infection as a long-term strategy.