Worm Parasites in Cattle: Welfare and Sustainable Control 2026

Gastrointestinal nematode parasites cause significant welfare problems in young cattle at pasture, requiring carefully managed control programmes.

Key Facts

Ostertagia and other nematodes are the most important parasites of grazing cattle, particularly calves in their first season
Type II ostertagiasis in late winter causes sudden onset severe diarrhoea and protein loss in young cattle
Hypobiotic larvae that overwinter in the abomasal mucosa activate in late winter, causing serious welfare emergencies
Anthelmintic resistance is increasing in cattle nematodes, making routine treatment less effective
Faecal egg counting and targeted selective treatment preserve refugia and slow resistance development

Welfare Considerations

Cattle worm welfare is shaped by parasite burden, individual immune status, and pasture contamination. Clinical parasitism causes profound welfare compromise - Type II ostertagiasis presents as sudden, severe disease in apparently healthy winter-housed cattle as hypobiotic larvae activate. The transition from heavy parasite challenge in the first grazing season to adult immunity requires careful management through that vulnerable period. Sustainable control that uses faecal egg counting, targeted selective treatment, and strategic pasture management maintains effective parasite control while reducing selection pressure for resistance, ensuring that effective welfare protection remains available in the future.

What You Can Do

Implement faecal egg counting before treating cattle to guide targeted selective treatment
Use worming pastures and mixed-age grazing to reduce parasite challenge for susceptible young cattle
Monitor cattle in their first grazing season closely for signs of parasitism
Work with your vet to develop a sustainable parasite control programme that slows anthelmintic resistance