Sheep Parasitic Gastroenteritis and Welfare

Parasitic gastroenteritis (PGE) caused by roundworms is a leading welfare and production challenge in sheep, exacerbated by anthelmintic resistance.

Key Facts

PGE caused by Haemonchus contortus and other nematodes is the primary welfare constraint in sheep globally.
Anthelmintic resistance — particularly to benzimidazoles and levamisole — is now widespread worldwide.
FAMACHA scoring of mucous membrane colour allows targeted selective treatment for Haemonchus infection.
refugia-based strategies maintain susceptible worm populations to dilute resistant gene frequencies.
Pasture management, including rested pastures and mixed-species grazing, reduces larval challenge significantly.

Welfare Considerations

Parasitic gastroenteritis causes weight loss, hypoproteinaemia (bottle jaw), anaemia, diarrhoea, and death in severe cases. Chronic subclinical infection impairs growth, reproductive performance, and immune function. The welfare impact is substantial and sustained in poorly managed flocks. The growing crisis of anthelmintic resistance threatens the primary tool for managing PGE, making strategic parasite management — rather than blanket dosing — essential. Integrated pest management approaches including targeted selective treatment, refugia, good pasture management, and genetic resistance breeding are the sustainable long-term solutions.

What You Can Do

Work with your vet to implement a strategic worm egg count programme rather than blanket dosing.
Learn FAMACHA scoring if you farm sheep in areas with high Haemonchus challenge.
Rotate anthelmintic drug classes appropriately to slow resistance development.
Consider breeding for genetic resistance using EBVs for FECRT (faecal egg count reduction).