Trace Minerals and Worm Burdens in Sheep: A Farmer's Guide

Article

The Hidden Link Between Trace Minerals and Worm Burdens in Sheep

With anthelmintic resistance known to be a growing challenge across UK and Irish flocks, sheep farmers are under pressure to rethink how they manage parasites. While drenches and wormers still have their place, a growing body of evidence is shining a light on something far more fundamental: trace mineral nutrition.

Sheep with inadequate levels of key trace elements—such as copper, cobalt, zinc, selenium and manganese—are consistently shown to be more vulnerable to parasitic infections. Minerals play a vital role in immune function, resilience and the body’s natural ability to keep worm burdens under control.

This article explores the science, the on-farm implications, and the practical steps farmers can take to improve both mineral status and parasite management.

Why low trace mineral levels increase worm burdens

When sheep are deficient in essential trace elements, their immune system becomes less effective. This reduced immunity allows gastrointestinal (GI) parasites to establish more easily and produce higher faecal egg counts (FEC).

The mineral–parasite connection: what we know

• Copper is a cofactor for enzymes such as superoxide dismutase (SOD), which helps immune cells kill pathogens. Low copper has been linked to reduced resistance to both bacterial and parasitic infections. In some breeds—such as Scottish Blackface—copper deficiency has historically been associated with high susceptibility to disease.
• Zinc deficiency weakens immunity and has been directly associated with higher worm burdens. Flocks with adequate serum zinc levels generally show lower FECs.
• Cobalt is essential for vitamin B12 production, energy metabolism and immune function. Low cobalt levels consistently result in higher FECs, poorer growth rates and weakened immunity.
• Selenium supplementation has shown improvements in antibody responses and immune activity in sheep.
• Manganese (Mn) has also been linked with reduced parasite levels, though more research is needed.

In natural grazing systems, sheep with higher innate mineral status—particularly copper and zinc—tend to carry fewer GI parasites.

Additional factors that influence parasite pressure

Mineral status isn’t the only contributor to worm burdens. Several environmental and management factors amplify the problem:

• Continuous or contaminated grazing leads to year-round parasite exposure.
• High stocking density increases pasture contamination.
• Stress from travel, weather extremes or late pregnancy weakens the immune response.
• Soil ingestion or brassica crops may cause imbalances in iron or other minerals, further affecting susceptibility.
• Sedentary flocks with little pasture rotation often show higher levels of infection.

It’s also important to note that animals may require higher mineral and vitamin levels to optimise immunity than what is needed for daily maintenance or growth.

Practical management to reduce worm burdens in sheep and lambs

Good mineral status must work hand-in-hand with sound grazing and flock management practices. The following strategies have proven particularly effective.

1. Clean grazing for lambs

Lambs can be weaned from around 12 weeks of age and should be moved onto cleaner, low-contamination grazing such as:

• silage or hay aftermath
• pasture previously grazed by cattle

This helps avoid early heavy exposure to infective larvae.

2. Keep lambs in tight age groups

Uniform age groups make FEC interpretation easier and allow for more targeted treatments. It also helps coordinate weaning and market-timing.

3. Use adult ewes strategically

After weaning, fit, mature ewes with low worm burdens can safely graze higher-risk pastures to help remove larvae through grazing and reduce long-term contamination.

4. Cross-species or rotational grazing

Mixed grazing—particularly sheep followed by cattle—reduces effective parasite pressure because most species-specific worms cannot complete their lifecycle in the wrong host.

5. Focus on body condition and nutrition

Sheep under nutritional stress cannot mount an effective immune response.

• Use body condition scoring (BCS) to guide management decisions.
• Supplement where necessary, but monitor closely to avoid metabolic issues or masking underlying parasite problems.

Feeding ewes high levels of undegradable protein around lambing can help reduce egg output in dung. Creep feeding lambs also supports immunity during critical periods.

6. Introduce bioactive forages

Plants such as chicory, sainfoin and birds-foot trefoil contain compounds that reduce the negative effects of parasitism and support overall gut health. Multispecies swards can play a major role in sustainable worm control.

7. Avoid winter dosing pitfalls

Treating ewes while housed can inadvertently spread resistant worm eggs onto pasture once they turn out again. Strategic timing is essential.

8. Use a leader–follower system

Allow lambs to graze ahead of ewes so they can access higher pasture and avoid grazing too close to the soil, where larvae are most concentrated. This significantly reduces worm intake.

Using wormers wisely

Anthelmintics remain necessary, but resistance is now a critical threat. Every farm must adopt a resistance-aware approach:

• Rotate wormer classes each season:
- - White drenches (benzimidazoles)Yellow drenches (levamisoles)
- - Clear drenches (ivermectins)
• Group sheep by size and weight to ensure correct dosing.
• Base treatments on FEC results rather than routine calendar dosing.
• Avoid under-dosing, as this accelerates resistance.

A more targeted approach helps protect the longevity of available products.

Building a resilient flock through nutrition and management

In the era of rising anthelmintic resistance, relying solely on wormers is no longer sustainable. The combination of optimal trace mineral nutrition, good pasture management, and strategic wormer use offers a far more robust and sustainable solution.

Healthy mineral status supports the immune system, reduces worm burdens naturally and helps sheep cope with parasite challenge throughout the grazing season. When combined with clean grazing, cross-species rotations and nutrition-focused flock management, farmers can significantly reduce reliance on drenches and improve long-term flock resilience.

References

NADIS (2009) Trace Element Deficiencies in Sheep. Reviewed 2016 by Phil Scott. National Animal Disease Information Service. Available at: https://www.nadis.org.uk (Accessed: 2 March 2026).

FAS (n.d.) Trace Element Supplementation in Sheep Flocks. Farm Advisory Service. Available at: https://www.fas.scot (Accessed: 2 March 2026).

Silk, L. (2016) ‘Subclinical diseases in sheep’, Vet Times. Available at: https://www.vettimes.co.uk (Accessed: 2 March 2026).