Dung beetle-mediated dung incorporation reveals hidden effects of veterinary drug residues on soil chemical attributes

Dung beetles are key drivers of nutrient cycling in livestock systems, yet the ecological consequences of veterinary drug residues for their soil-building functions remain poorly understood. Here, we evaluated how dung incorporation by the dung beetle Dichotomius bos affects soil chemical attributes, and whether residues of ivermectin or levamisole in cattle dung modify these responses. In a 31-day laboratory experiment, individual beetles were exposed to dung from untreated, ivermectin-treated, or levamisole-treated cattle across eight replicates per treatment, and soil chemical attributes, including organic matter, carbon, macronutrients, pH, and effective cation exchange capacity (ECEC), were analysed at the end of the experiment. In the first analytical approach, beetle-dung treatments were compared against a soil-only control using treatment-level models; only potassium differed significantly, with higher concentrations in the ivermectin treatment. In a second approach, restricted to beetle-dung treatments, total dung incorporation was included as a continuous covariate. Greater incorporation was associated with higher levels of organic matter, carbon, magnesium, phosphorus, base saturation, and effective cation exchange capacity (ECEC), but with lower potential acidity. This approach also revealed drug-specific effects invisible to categorical comparisons: ivermectin maintained elevated potassium independently of incorporation rate, while levamisole negatively affected both phosphorus and calcium availability. These results indicate that the intensity of dung beetle-mediated dung incorporation is an important determinant of several soil chemical attributes under controlled experimental conditions, and that veterinary drug residues can partially disrupt these processes through nutrient-specific pathways. Critically, many of these effects only became detectable when the intensity of biological activity was explicitly modelled, highlighting the importance of process-level variables in assessments of soil fauna contributions to ecosystem functioning.