Summary
This controlled field trial in Romney-cross wethers demonstrated that artificial infection with Haemonchus contortus at medium (4000 L3) and high (8000 L3) doses produces dose-dependent physiological impairments including anaemia, elevated inflammatory cytokine concentrations, and reduced liveweight gain, whilst behavioural changes were not detected. The findings suggest that gastrointestinal nematode burden above a threshold level compromises lamb welfare and production performance despite minimal overt behavioural indicators, with implications for parasite management in grazing systems.
UK applicability
These findings are directly applicable to UK sheep farming, where H. contortus infection of grazing lambs remains a production and welfare concern. The identification of physiological threshold effects informs parasite control strategies and highlight the importance of monitoring internal indicators of infection burden rather than relying on behavioural observation alone.
Key measures
Faecal egg counts (epg); red blood cell count, haemoglobin, haematocrit, mean corpuscular volume; IL-6 concentration; liveweight gain; behavioural observations (video and accelerometry)
Outcomes reported
The study measured faecal egg counts, blood parameters (red blood cells, haemoglobin, haematocrit, mean corpuscular volume), cytokine concentrations (IL-6), liveweight gain, and behavioural responses in lambs artificially infected with varying doses of H. contortus larvae over a 6-week period.
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