The influence of veterinary medicines on the decomposition of dung organic matter in soil

Six commonly used veterinary medicines were investigated for their influence on the decomposition of dung from treated cattle. Recommended doses of the antibacterial agents spiramycin and enrofloxacin, and of the antiparasitic compounds α-cypermethrin, fenbendazole, ivermectin and levamisole were given to heifers. Dung was collected prior to treatment and two days after treatment, and mesh bags with portions of 40 g of dung were placed in the soil. The organic matter was determined in mesh bags retrieved after 8, 12 and 16 weeks. When compared with dung from untreated cattle, the mean loss of organic matter was significantly lower in dung collected from heifers dosed with α-cypermethrin, fenbendazole, ivermectin, levamisole and spiramycin but not in dung from heifers treated with enrofloxacin. Ivermectin and spiramycin caused a reduced loss for all time intervals, i.e. for 0–8, 0–12 and 0–16 weeks. Levamisole and α-cypermethrin resulted in significant effects when measured over 0–12 and 0–16 weeks, whereas fenbendazole significantly reduced loss of organic matter for the time interval 0–16 weeks only. When an exponential decay model was applied to the data, all veterinary medicines, except spiramycin, resulted in significantly more organic matter remaining at infinite time, as estimated by the parameter b/a.