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no similar information has been published on the sale of equine ec- toparasiticide treatments.
MITIGATING ENVIRONMENTAL DAMAGE Dung beetles, therefore, play an important role in improving
While the overall environmental impact of equine antiparasitic treat- ments is unknown, negative ecological effects have been documented in multiple species for many of the same pharmaceuticals used in horses. Pesticides are designed to target biochemical processes in specific pests, but these processes are often common pathways shared among many different species. Thus, injudicious use of pesti- cides may lead to serious impacts on nontarget species (Preston- Allen et al., 2023 ). According to the UK Parliament, residues of veterinary medicines, including anthelmintics and ectoparasiticides, are a contrib- utory factor to the decline in insect populations and diversity in the UK, leading some species to extinction (Wentworth & Robertson, 2020 ). Much research in production animals has focused on dung bee-
tles as a marker of biodiversity and environmental damage (Bicknell et al., 2014 ). However, as outlined by Beynon et al. ( 2015 ), dung bee- tles also provide considerable value to the UK cattle industry (esti- mated at £367 million each year) through the provision of a number of important ‘ecosystem services’, including:
• provision of biomass and reduced nutrient leaching (reducing the need for fertiliser and improving crop yields);
• regulation of pests, gastrointestinal parasites and disease: small endocoprid dung beetles can reduce the development and sur- vival of livestock gastrointestinal parasites on pastures, thus re- ducing the number of infectious larvae available for re- infection of grazing cattle (Sands & Wall, 2017 );
• formation of soil through increased nutrient cycling, increased soil structure, gaseous exchange and drainage, and reduced compaction.
cattle pastures and reducing the risk of diseases caused by gastro- intestinal parasites. In contrast, the role that dung beetles play in horse pastures, where pasture hygiene (‘poo- picking’) is commonly performed, is currently poorly understood.
THE ENVIRONMENTAL IMPACT OF ENDOP ARA SIT ICI DES
Once administered to animals, endoparasiticide (anthelmintic) drugs may be metabolised to other active and/or toxic metabolites (Danaher et al., 2007 ), with both parent drugs and metabolites primarily entering the environment through direct excretion during grazing. Once in the environment, anthelmintic drugs may also undergo further degradation to transformation products (Horvat et al., 2012 ). The major concern is the effect of these products on nontarget organisms, including ter- restrial invertebrates, such as dung beetles (Jacobs & Scholtz, 2015 ; O ' hea et al., 2010 ) and aquatic animals (Liebig et al., 2010 ; Sanderson et al., 2007 ). A summary of the known ecotoxic effects of the com- monly used equine anthelmintics is shown in Table 1 .
IVERMECTIN
Ivermectin belongs to the avermectin family of compounds. These are effective, broad- spectrum macrocyclic lactones widely used for control of parasitic infections in cattle, pigs and horses. In
TABLE 1 Summary of the ecotoxic effects of commonly used parasiticide drugs in horses. Drug name
Route of excretion
Moxidectin Faeces Principal metabolite Unmetabolised moxidectin
HASELER ET AL.
The presence of dung beetles has been shown to have an important role in soil nutrient cycling, plant productivity and hydrological func- tioning (Keller et al., 2022 ), the latter being essential for precipitation management and reduction of surface water run- off.
Duration of excretion
>75 days
Toxicity
Less toxic to invertebrates than ivermectin
(freshwater animals) (fish)
Ivermectin Faeces Unmetabolised ivermectin >40 days
Dung- degrading invertebrates
Freshwater animals Fish Dogs
Pyrantel Fenbendazole Doramectin
Faeces Faeces
Faeces Unknown Fenbendazole sulfoxide (oxfendazole) Unmetabolised doramectin
Unknown 4–5 days
>60 days Unknown
Freshwater animals Fungi
Dung- degrading invertebrates
Freshwater animals Fish
Praziquantel Faeces Unknown Unknown Unknown (low toxicity)
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