Effects of ivermectin and doramectin faecal residues on the invertebrate colonization of cattle dung

Abstract

The effects of avermectin [ivermectin (IVM) and doramectin (DRM)] faecal residues on dung colonization and degradation by invertebrates were evaluated during late spring in the east of La Pampa province, Argentina. The study was conducted after collection of faecal material from animals (10 steers per group) allocated to the following groups: untreated control group (CG) and groups treated subcutaneously (200 μg/kg) with either DRM (DG) or a long‐acting formulation of IVM (IG). Fifty pats (550 g each) per group were collected, prepared and deposited on the field on days 3, 7, 16 and 29 post‐treatment (pt). Eight pats per group were recovered after 7, 14, 21, 42, 100 and 180 days post‐deposition (pd) on the field. The weight, percentage of dry matter, number of arthropods and nematodes from faeces were determined. The faecal concentrations of IVM and DRM were measured by high performance liquid chromatography (HPLC) throughout the trial period to correlate the pattern of drug degradation in dung with pd time. The total number of arthropods in dungs from CG was higher (P < 0.05) than those counted between days 3 and 29 pt in IG and DG. A decrease in the number of Coleoptera larvae (P < 0.05) between days 21 and 42 days pd was observed in both treated groups. Diptera larvae counts in CG pats were significantly higher (P < 0.05) than those obtained in treated groups in the 7‐ and 14‐day‐old pats. A lower number (P < 0.05) of Collembola, compared with pats from CG, was recovered from IG and DG pats deposited at days 3 and 7 pt and exposed from day 42. The counts of Acari in pats from treated animals were lower (P < 0.05) than those observed in CG pats at 3, 8 and 16 days pt. There were no differences neither in adult Scarabaeidae recovered nor in the proportions of dung buried and destroyed by great dung beetles. Dung specific nematodes were reduced (P < 0.05) in IG and DG pats from 3 and 7 days pt compared with those of CG pats. The comparative results shown here demonstrate that the negative effects of both IVM and DRM on dung colonization are similar. The pattern of drug degradation in the environment was very slow. High residual concentrations of both active parent compounds were recovered in dungs exposed in the field for up to 180 days pd. Concentrations as high as 13 ng/g (IVM) and 101 ng/g (DRM) were measured in faeces obtained from pats deposited on day 27 pt and exposed to the environment during 180 days. The results show a decrease in invertebrate colonization of dung recovered from IVM‐ and DRM‐treated cattle, which is in agreement with the large drug residual concentrations measured in faeces.

Environmental impact of ivermectin excreted by cattle treated in autumn on dung fauna and degradation of faeces on pasture

“…In agreement with Sommer et al (1992) and Suárez et al (2003), the highest concentrations of ivermectin were detected 3 days after treatment. Meanwhile, the concentrations in faecal samples collected 1 and 3 days after treatment were significantly higher than in those collected later, regardless of the period of environmental exposure.…”

“…In addition, the drug concentrations at 7 dpt were also higher than those collected afterwards. Ivermectin concentrations in the present study were higher than those detected in La Pampa province for similar after-treatment and afterdeposition times (Suárez et al 2003). These differences could be explained by the different experimental models used in both investigations, as well as by the different seasonal conditions in both regions.…”

“…Barth (1993) suggests using the organic matter content to measure this effect given that climatic conditions can affect other physical measurements. Significant differences were found in the weight of faecal pats deposited in autumn in the semi-arid Pampean region (Suárez 2002), but not in spring (Suárez et al 2003), which led the authors to conclude that the drug had no effect on faecal degradation (Suárez et al 2003). The contradictions in these two studies suggest that (a) a seasonal effect on behaviour and diversity of dung organisms could exist and (b) it is necessary to evaluate the impact on faecal degradation following a homogeneous standard.…”

“…The findings of ivermectin effects on soil organisms have been controversial (Halley et al 1989a;Gunn and Sadd 1994;Svendsen et al 2002;Jensen et al 2003). During parasite control programs conducted in South America, Iglesias (1998) found that ivermectin in faecal pats of subcutaneously treated cattle in tropical climate reduced the numbers of immature Cyclorrapha (Diptera), adults and larvae of Polyphaga (Coleoptera), and Acari; while Suárez et al (2003) observed the reduction effect of the drug on soil nematodes during late spring to early autumn in the west (semi-arid) Pampean region of Argentina.…”

Semifield assessment of the runoff potential and environmental risk of the parasiticide drug ivermectin under Mediterranean conditions

“…These results indicate slow degradation of Iv in dung and agree with previous field studies. Suarez et al (2003) suggested DT 50 s of up to 180 days in cattle dung (180 days after deposition of the dung pats, 10-57% of the initially applied Iv concentration was detected), and Sommer et al (1992) observed no biodegradation within 45 days. Table 3 shows the measured concentrations in soil at the end of the experiment.…”