Gastrointestinal nematodes (GINs) represent the most significant parasitological challenge in sheep farming worldwide, causing substantial welfare impacts and economic losses. The primary culprit, Haemonchus contortus (barber's pole worm), is a blood-sucking parasite capable of killing sheep rapidly in warm climates.
Heavy parasite burdens cause anaemia, hypoproteinaemia (bottle jaw), weight loss, lethargy, and death. Even subclinical infections impair feed conversion efficiency, suppress immune responses, reduce reproductive performance, and compromise overall animal wellbeing. Sheep experiencing significant parasite burdens show reduced activity, social withdrawal, and impaired grazing behaviour.
The FAMACHA (FAMacha) scoring system, developed in South Africa, provides a practical field tool for assessing anaemia caused by H. contortus. By examining conjunctival mucous membrane colour on a 1-5 scale, farmers can identify individuals requiring treatment versus those with adequate resistance. This targeted selective treatment (TST) approach reduces anthelmintic use while maintaining animal welfare.
Resistance to all major anthelmintic classes (benzimidazoles, levamisole, macrocyclic lactones) is widespread globally, threatening our ability to control parasites chemically. Multi-drug resistance is increasingly common. Responsible use protocols—including refugia-based management (leaving untreated animals to maintain susceptible parasite populations), accurate dosing, and avoiding unnecessary treatments—are essential for preserving drug efficacy.
Sustainable control requires integrating multiple strategies: genetic selection for parasite resistance (using EBVs for Faecal Egg Count), pasture management (avoiding overgrazing, using mixed-species grazing), nutritional support (adequate protein maintains immune function), and biological control through copper oxide wire particles or nematophagous fungi. Quarantine treatments for incoming animals prevent introduction of resistant strains.
Regular faecal egg counts (FECs) are the cornerstone of evidence-based parasite management. Monitoring egg counts helps assess treatment efficacy, identify resistance, and time treatments appropriately. Body condition scoring and FAMACHA assessments complement FECs in field settings where laboratory testing is impractical.
Effective parasite control directly improves sheep welfare by preventing suffering from anaemia and malnutrition, maintaining body condition, supporting normal behaviour, and reducing mortality. Sustainable management approaches that preserve anthelmintic efficacy are essential for long-term animal welfare protection.