There has been considerable interest in the short-term environmental impacts of anthelmintic residues in faecal material, which have been shown to reduce invertebrate populations and decomposition rates, invertebrate numbers and rates of faecal breakdown were investigated on two organic and one conventionally managed farms, which had not used anthelmintics within the previous six months but had different histories of long-term use. Invertebrate populations were sampled using pitfall trapping. Relative breakdown rates were estimated using Perspex strips containing ten holes filled with sheep faeces, these were recorded until all the holes were emptied. Significant differences were found in invertebrate populations and breakdown rates. The largest invertebrate populations and fastest rates of faecal decomposition were found at the established organic farm with a history of minimal anthelmintic use. The lowest numbers of invertebrates and slowest decomposition rates occurred on the more recently established organic farm, which formally regularly used anthelmintics, and currently uses them in targeted and reduced amounts. Within farms, semi-natural grasslands were generally found to support more invertebrates than improved pastures. Decomposition rates were fastest in improved pastures in autumn, and in semi-natural pastures in spring. However, the established organic farm was unusual in that more invertebrates were found in the improved pasture than the semi-natural pasture, in both seasons, and the fastest breakdown rates were associated with the improved pasture. Over farms and pasture types, decomposition rates were significantly correlated with invertebrate populations, with this relationship being closer in spring than in autumn. The results suggest that farm-to-farm variation in invertebrate numbers and decomposition rates may be of greater magnitude than the difference between organic and conventionally managed farms. Alternatively, the results may suggest anthelmintic use may have long-term effects suppressing invertebrate populations and decomposition rates. Organic farmers may have to wait many years for invertebrate populations to recover from previous applications of anthelmintic. Perhaps maintaining populations of coprophagous invertebrates and rapid decomposition rates may form part of an integrated pest control for intestinal parasites, by encouraging breakdown before parasite larvae have chance to develop.