Does Doramectin Use on Cattle Indirectly Affect the Endangered Burrowing Owl

Abstract

Doramectin is one of several endectocide compounds widely used to treat nematode and arthropod pests affecting cattle. Insecticidal residues in dung of endectocide-treated cattle can reduce numbers of dung-breeding insects. Concerns have been raised that use of endectocides may adversely affect birds that rely on dung-breeding insects as food. However, these concerns have not been specifically addressed in previous studies. We performed two studies to collectively assess whether doramectin adversely affects burrowing owls (Athene cunicularia Molina), which are listed as ''Endangered'' in Canada. In the first study, insect emergence was monitored from dung of cattle treated with a recommended topical dose of doramectin. Experiments replicated in each of 3 yr showed residues reduce the number of insects developing in dung of cattle treated up to 16 wk previously. In the second study, we identified prey items from regurgitated pellets collected at 206 burrowing owl nests in southern Alberta and Saskatchewan, Canada. A total of 50 213 prey items were identified, of which 90% were invertebrates. Beetles (Coleoptera) comprised 54% of the total prey items, followed next in abundance by grasshoppers (Acrididae, 20%) and crickets (Gryllidae, 16%). Of the beetles, 1 381 specimens were identified as breeding in dung (mainly species of Aphodius, Canthon, Onthophagus). The dung beetles comprised an estimated 2.8% of the total prey items or 0.1% of total prey biomass. Results of the first study validate initial concerns that doramectin use can reduce numbers of insects breeding in dung of treated cattle. Results of the second study show reliance of burrowing owls on dung beetles is sufficiently low that use of doramectin on cattle is unlikely to appreciably affect the food supply of co-occurring burrowing owls. Resumen El doramectin es uno de varios compuestos endectocidos ampliamente usados para tratar las pestes de nemátodos y artrópodos que afectan el ganado. Los residuos de insecticidas en el estie´rcol del ganado tratado con endectocidos pueden reducir el número de los insectos encontrados en el estie´rcol. Existe preocupación de que el uso de endectocidos podría afectar negativamente a aves que dependen de insectos de estie´rcol como alimento. Sin embargo, estas preocupaciones no se han abordado específicamente en los estudios anteriores. Nosotros hemos realizamos dos estudios para evaluar colectivamente si el doramectin afecta adversamente a la lechuzita terrestre (Athene cunicularia Molina), el cual esta listado como ''en peligro de extinción'' en Canadá. En el primer estudio, la aparición de insectos fue monitoreada en estie´rcol de ganado tratado con una dosis actual recomendada de doramectin. Los experimentos repetidos en cada uno de los tres añ os mostraron que los residuos redujeron el número de insectos que se desarrollan en estie´rcol en ganado tratado hasta por 16 semanas. En el segundo estudio, nosotros identificamos ítems del pellets regurgitados de la lechuzita terrestre desde abril a finales de julio de 200...

Validation of a standard field test method in four countries to assess the toxicity of residues in dung of cattle treated with veterinary medical products

“…Similarities were greater when comparisons were restricted to the same taxa. For example, flies in family Sepsidae are extremely sensitive to residues of IVM and related compounds, with similar but somewhat lower sensitivities exhibited by flies in family Sphaeroceridae . The same finding was obtained in the present study at sites where recovery of these taxa allowed for statistical analyses (i.e., Lethbridge, Montpellier, and Wageningen; Table ).…”

How to test nontarget effects of veterinary pharmaceutical residues in livestock dung in the field

“…The dung is frozen until collections are completed, then thawed to permit simultaneous comparisons among different collections of dung; e.g., dung collected pretreatment versus dung collected 1 and 2 weeks posttreatment (Floate 1998b;Floate et al 2002Floate et al , 2008. This method requires fewer animals than the first method and eliminates intergroup variation as a potential confounding factor.…”

“…Topical application of some VMPs may result in fecal excretion of insecticidal residues for extended periods; e.g., over 16 weeks for doramectin (Floate et al 2008) and over 12 weeks for ivermectin (Floate 1998b). Animals treated with sustained-release devices may excrete insecticidal residues for periods exceeding 100 to 150 d (Errouissi et al 2001;Wardhaugh et al 2001a;Wardhaugh et al 2001b).…”

“…The nontarget effect of fecal residues can be assessed by recording the number of insects developing in dung pats that have been exposed in the field and then held in cages for insect emergence (Floate 1998b;Floate et al 2002Floate et al , 2008. Pats exposed for a short period may exclude some species that are attracted to old dung; e.g., some species of Aphodius beetles.…”

“…Numerous studies have assessed the effects of VMPs on dung organisms, both in the laboratory and in the field, using different methods (reviews by Floate et al 2005;Lumaret and Errouissi 2002;Wardhaugh 2005;also Floate 2007;Floate et al 2008;Hempel et al 2006;Iwasa et al 2007Iwasa et al , 2008Kryger et al 2005Kryger et al , 2007Lumaret et al 2007;Rö mbke et al 2007Rö mbke et al , 2009Suárez et al 2009;Webb et al 2007Webb et al , 2010. Collectively, these studies support the following conclusions: 1) there has been a strong bias for research on endectocides, primarily ivermectin but also doramectin, eprinomectin, and moxidectin; 2) most of the research studies have been performed in Europe, Canada, and Australia, and to a lesser extent in Japan, South Africa, South America, and the United States; 3) the lethal effects of residues on species of dungbreeding flies and beetles in cattle dung are most often measured; 4) because insect activity can accelerate dung pat degradation, the effect of residues on the rate of dung decomposition also is often measured in field-based studies; 5) the lack of standard test methods and reporting protocols largely prevents direct comparisons among studies; and 6) the interpretation of results is generally hampered and easily confounded by a lack of knowledge about the local biological aspects of the study system, i.e., the dung pat and its associated organisms, which may vary considerably among geographic regions.…”