Effects of ivermectin on pastureland ecology

Disintegration of dung pats from cattle treated with the ivermectin anthelmintic bolus, or the biocontrol agent Duddingtonia flagrans

An experiment was performed during the grazing seasons of 1998, 1999 and 2000 to study the influence of the antiparasitic drug ivermectin and the nematophagous fungus Duddingtonia flagrans on cattle dung disintegration. The faeces originated from groups of animals that were part of a separate grazing experiment where different control strategies for nematode parasite infections were investigated. Each group consisted of 10 first-season grazing cattle that were either untreated, treated with the ivermectin sustained-release bolus, or fed chlamydospores of D. flagrans. Faeces were collected monthly on 4 occasions and out of pooled faeces from each group, 4 artificial 1 kg dung pats were prepared and deposited on nylon mesh on an enclosed pasture and protected from birds. The position of the new set of pats was repeated throughout the 3 years of the study. Each year, the dung pats were weighed 4, 6, 8 and 10 weeks after deposition and immediately afterwards replaced to their initial positions.

Results showed that there was no difference in faecal pat disintegration between groups. However, the time-lag between deposition and complete disintegration of the faeces varied significantly between deposition occasions. Dung pats disappeared within 2 weeks (visual observation) when subjected to heavy rainfall early after deposition, whereas an extended dry period coincided with faeces still remaining 12 months after deposition.

Reductions of non-pest insects in dung of cattle treated with endectocides: a comparison of four products

Pour-on formulations of four endectocide products were compared to assess the effect of faecal residues on insects developing in naturally-colonized dung of treated cattle. In each of three independent experiments, suppression of insects was associated with application of doramectin, eprinomectin and ivermectin, but no effect was observed for moxidectin. When data were combined across experiments to increase sample sizes, suppression of insects was observed for each compound, with the least effect being observed for moxidectin. Based on the number of species affected and duration of suppression, doramectin > ivermectin > eprinomectin >> moxidectin were ranked in descending order of adverse effect. A second set of three independent experiments was performed to assess the effect of endectocide treatment on dung degradation. Delayed degradation was observed for dung of cattle treated with doramectin, eprinomectin and moxidectin in the first experiment. No effect of treatment was detected in the second experiment. An effect of moxidectin was detected in the third experiment, but differences could not be detected with subsequent post-hoc tests. When data were combined across experiments to increase sample sizes, delayed degradation was detected only for eprinomectin. The apparent discrepancy between the low effect of moxidectin on insects versus its effect of dung degradation suggests the confounding action of other unidentified factors. Results of the current study indicate that use of moxidectin is least likely to affect the natural assemblage of insects associated with cattle dung.

Endoparasite control strategies: implications for biodiversity of native fauna

Efforts to control the spectrum of diseases that affect humans, our crops and our animals pose problems which need to be debated openly. Widespread use of chemicals in such a broad sphere raises important concerns not only about safety for the users, consumers and target species, but especially about the not so obvious effects upon the ecosystems in which they are used. Some undetermined level of biological diversity is necessary to maintain ecological function and resilience. These, in turn, are necessary for generating the biological resources (trees, fish, wildlife, crops) and ecological services (watershed protection, air cleansing, climate stabilisation, erosion control) on which economic activity and human welfare depend. The driving forces behind decline of biodiversity stem entirely from human activities. Underlying causes are those resulting from the cultural and social factors associated with economic activities and lead to direct depletion of species, and degradation or destruction of habitats. The broad spectrum and high efficacy of the macrocyclic lactones against nematode and arthropod parasites of livestock and companion animals are unprecedented. Cattle, horses, sheep, swine, dogs--to varying degrees all are utilised by humans for economic gain. Detrimental impact upon non-target animals is considered acceptable in eradicating parasites because of their economic importance to commercial livestock production. Production will increase when these parasites are eliminated, but we remain oblivious to the long-term consequences of our actions. What are the ecological limits to rural economic activities? Decomposing animal faeces help to maintain our ecosystem by returning valuable nutrients to the soil. Dung fauna-fungi, yeast, bacteria, nematodes, insects and earthworms--play a non-conspicuous but important and varied role in this decomposition process, a role dependent upon many factors, especially environmental ones. Anthelmintics and pesticides are of considerable value in agriculture, but largely at an unevaluated cost to the greater environment. We have insufficient knowledge of the extent to which a spectrum of anthelmintics and pesticides affect ecological function and ecosystem resilience in our commercial plant and animal production systems. It is time we developed a genuine interest in avoiding "the dialogue of the deal" that in the past has minimised interdisciplinary research between environmental ecology and commercial plant and animal production.