Trojan horses (and cows and cats and dogs…)

© Ben Hall/2020VISION

Ever considered ways our domestic animals may impact wildlife, the environment, and our beleaguered insect populations?

We love our animals! There are nearly a million horses in the UK, and about a quarter of households have one or more dog. It is estimated globally that livestock ‘biomass’ is fifteen times higher than that of wild mammals. I am not going to talk about the carbon footprint of livestock or pets … I’m not going to talk about predation and disturbance to wildlife that can be caused when our pets roam free… instead I want to highlight some unexpected ways our domestic animals may impact wildlife and the environment, especially our beleaguered insect populations.

One way we express our love for our four legged friends is to dutifully pay vet bills and buy medicines: wormers, flea and louse treatments, antibiotics… Parasites cut productivity in livestock and treating animals with medicines may boost farmers’ yields and profit margin.

The result is a costly cocktail we often don’t question the need for – but where do many of these powerful pesticides and medicines end up? All too often in our natural environment.

Domestic horses and cattle are regularly given powerful anti-worming medicines known as Ivermectins. Standard advice is to keep horses in a stable for a couple of days after administering the drugs, but this is not always done. So what when they are returned to pasture again? Very often the dung contains high residues of ivermectins which, having killed intestinal worms, go on to kill the myriad wild invertebrates waiting to recycle the nutrients to the soil and underpin the food chain. The result is sterile soil and a contribution to the collapse in insects which would feed birds like swallows and pollinate our crops. Even if animals are kept in stables, what happens to the dung? It is often used as manure, and in using it we may perhaps unwittingly be killing our friends such as garden earthworms.

This is an especially crucial issue in the New Forest, where there are many rare and specialised insects and invertebrates many of which depend on dung. We simply don’t know what the ecological consequences are if medicines are used without great care. Often livestock gather to drink from ponds and if they deposit dung with medicines in, the impacts on the Forest’s rare invertebrates such as the medicinal leech, could be huge. If we don’t pick up after our dogs, we are not only creating a nuisance and fertilising the soil to the detriment of wildflowers, we may be contaminating the soil with powerful chemicals that literally kill its life. One reason why the ‘stick and flick’ approach is not acceptable.

Mayfly

© Katrina Martin / 2020VISION

During hot weather, dogs love nothing more than to have a swim. Also, as pet owners know, fleas are abundant in the warm weather… so when our dogs, which are given powerful insecticides in the form of flea louse and tick powders, take a swim in one of our rivers, much of it gets washed away! Some experts believe this, combined with livestock medicines, could be one of the causes of a collapse in the all-important riverflies seen in our chalk rivers: the natural abundance of mayflies, freshwater shrimps etc. which underpin the food chain but are disappearing rapidly. I noticed recently that poultry feed contains anti-worming drugs as standard whether needed or not. Might our free-range hens and reared gamebirds be releasing these powerful chemicals into the soil, resulting in insect declines over significant areas of woodland and farmland?

We at the Wildlife Trust do not want to poo-poo animal husbandry. We actually have our own livestock. But we are careful to use resilient breeds, fed on flower-rich pastures, which require fewer medicines. When we have to give medicines, we carefully ensure that treated livestock are not able to release medicines into our sensitive habitats through quarantine. There is some evidence that livestock ‘self-medicate’ by selecting certain wild plants if they have parasites. This is not possible for most factory-farmed animals fed on intensively grown cereals and soya.

If we continue to keep domestic animals in large numbers, perhaps we can all do something to help avoid the so-called ‘insect apocalypse’ in subtle but important ways. Experts agree that we should eat less meat and dairy to help protect the environment – if we do that there will be fewer impacts on our wild insects too. If we do eat meat or dairy products, organic production involves using fewer vets’ medicines. If we own animals we should certainly use vet medicines sparingly, not prophylactically, and this will reduce the risk of drug resistance in parasites too.  If we let animals out in the countryside we can make sure that they have not recently been dosed with anti-parasitic drugs and powders, or if they have, that we don’t let them swim in rivers and waterbodies. We should, of course, always pick-up after our dogs, but that’s not really practical for horses, which like the Trojan myth, may contain a hidden and deadly payload…

What have insects - yellow dung fly (Vaughn Matthews)

© Vaughn Matthews

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