Currently over 6 million doses of endectocides (predominantly ivermectin, a persistent, broad-spectrum antiparasitic drug) are administered annually - mainly to young cattle - in the Republic of Ireland (Murphy, 2000; Daly, 2002). Most of the ivermectin is ultimately eliminated in the faeces where it is an effective insecticide, controlling the larvae of dung-breeding flies (Madsen et al. 1990; Hill, 1995; Fahy, 1999). However, because of its potency and broad spectrum of activity, concerns arise in regard to unintended environmental effects on non-target organisms, notably beneficial groups such as dung beetles and earthworms whose activities are important for the decomposition of dung pats (Holter, 1996, 1997, 1998; Holter and Sommers, 1998; Fahy, 1999). Since cattle dung represents a major source of organic nitrogen in intensively-grazed pasture, “any effects of ivermectin on dung fauna and dung decomposition could have significant implications for nitrogen cycling”. Effects of ivermectin on the ecology of the dung fauna, dung decomposition and nitrogen cycling have each been studied in several separate studies. As Fahy (1999) pointed out “there is an urgent need for an integrated systems-level approach” to such studies.
