Dung dispersal and grazing area following treatment of horses with a single dose of ivermectin.

The study investigates the environmental impact of treating horses with the recommended dosage of ivermectin, focusing on the effect on dung dispersal rates and grazing areas. Results indicate a delayed dung dispersal and increased grazing area loss when horses were treated with ivermectin.

Experiment Design and Methodology

• The research involved two controlled experiments, conducted in Ohio, with 29 horses in total.
• In 1988, the researchers measured dung dispersal rates by tracking the changes in dry weight over time of dung piles, or copromes, collected from four treated and four control horses three days post ivermectin treatment.
• In 1989, the team compared the effects of treating horses with oral ivermectin or oxibendazole to untreated controls. This part of the study encompassed 21 horses under natural grazing conditions, with measurements taken periodically from June to the following March. They measured dung pat circumferences to assess differences in dispersal rates.

Key Findings

• Results showed a delay in the dispersal of dung piles from horses treated with ivermectin in June, leading to significantly heavier ivermectin copromes compared to control horses by September. No difference was observed following the treatment in August.
• In the 1989 study, data indicated significant differences in dung pat diameters between horses treated with ivermectin and untreated and oxibendazole-treated horses.
• Reductions in mean dung pat diameters did not occur for ivermectin dung pats until October, and even then, the reduction was significantly less than the reduction for control and oxibendazole dung pats.
• By the end of the study, there was a 24.7% reduction in ivermectin dung pats, lower than the reductions seen in untreated (59.1%) and oxibendazole-treated (59.9%) horses.
• Horses treated with ivermectin had significantly more dung pats showing complete dispersal in oxibendazole or control plots than in ivermectin plots.

Implications and Conclusions

• These findings suggest that treating horses with ivermectin leads to delayed dung dispersal and greater grazing area loss, which have potential implications for pasture management and environmental health.
• It is hypothesized that the environmental effects associated with ivermectin treatments could potentially be mitigated by more rational use of anthelmintics, thereby reducing the drug’s negative impact on both individual horse health and the overall ecosystem balance.