Livestock husbandry - chemical control of parasites (endectocides)
There are many insects associated with the breakdown of livestock dung.
Cattle dung in particular supports a large variety of insects, which in turn support many bird and mammal species.
Some of the drugs (endectocides) administered to livestock to control parasites retain insecticidal residues in their dung, which can affect the development and survival of insects involved in the breakdown of dung. This not only impacts the insect species that directly use the dung but also associated species who in turn feed on them.
Of particular concern are avermectins, the collective term for the active ingredients in a range of animal health products.
Chemical concentrations in the dung are highest in the first few days after treatment but can be present for several weeks and toxic effects have been recorded over 140 days post-treatment.
Minimising the use of avermectins to remove the adverse effects of this toxicity will bring benefits for a range of species, including several of high conservation concern. The dung produced by livestock supports a diverse community of invertebrates, some of which are of conservation interest in their own right such as hornet robberfly, and many of which provide an important food source for other animals. These include birds such as swallows, lapwings choughs and wagtails, mammals such as hedgehogs and shrews and several bat species including some that are highly reliant on such insects.
Importantly for farming, the action of insects has an important role in breaking down the dung and in doing so returning the nutrients to the soil as well as keeping the pasture clean for grazing.
Avermectins are a valuable resource in the long-term control of parasites, their rotation with other chemical groups helping to prevent the development of resistance. The potential impacts of avermectins can be reduced by trying to maximise the amount of avermectin-free dung available during the spring and summer. The ways this could be achieved will vary between farms, but could involve one or more of the following approaches.
Ways to minimise the impacts of endectocides
Treat livestock only when necessary and avoid treatment of older animals if they are not susceptible to the parasite of concern (this may include assessment of parasite burdens before treatment, for example by faecal egg count assays or FAMACHA).
Treat livestock with non-avermectin products that are effective against the parasite to be controlled.
If using an avermectin product select one that has less impact on dung insects such as those based on milbemycins (moxidectin).
Graze avermectin-treated livestock in fields close to others containing untreated animals to ensure untreated dung is nearby;
Where possible, alter the timing of use of avermectin products to avoid the main period of wildlife activity in the spring/summer, for example treating livestock when they are housed.
On habitats of particular importance (e.g. old grassland, or where important insects, birds or mammals occur), a precautionary approach could be adopted of grazing with livestock that have not been treated with avermectins in the previous 2 to 3 weeks.
Adopt animal husbandry and grassland management practices that help to reduce the use of chemical treatments. These include:
- Maximising the benefits of ‘clean grazing’ provided by mixed cattle/sheep systems, hay/silage aftermaths and new grass leys.
- For some parasites, it may be possible to leave a small percentage of less susceptible livestock untreated e.g. older livestock in good body condition.
- Optimise timing of treatment by observing disease forecasts and monitoring worm egg counts in faecal samples.
- Ensuring correct dose rate and administering effectively.
- Regularly review the list of approved chemicals and their relative toxicity.
Here are some useful case studies and articles about how farmers are putting Farm Wildlife into practice on their farms
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