Veterinary antibiotics (VAs) contamination as a global agro-ecological issue: A critical view

Veterinary antibiotics (VAs) are used worldwide in animal fanning as drugs to treat or prevent diseases and serve as feed additives. VAs are usually poorly sorbed in the animal gut, and the majority are excreted unchanged or as their recalcitrant metabolites in feces and urine. More importantly, animal wastes are frequently employed in agriculture as a supplement to fertilizer, raising a major international concern about the potential impacts of VAs on agro-ecosystems. Increasing use of these manures in agriculture is thus posing a threat in the form of rapid increase in antibiotic resistance. The current review critically summarizes available literature on the global consumption, exposure pathways, occurrence, fate and environmental effects of VAs in manure-fertilized agricultural soils. Recognizing the importance of the issue of VA resistance in the environment, we focused on the increased abundance and transferability of VA resistance determinants, highlighting details as to how they contribute to the change in human microbiome. Notably, existing regulations and research gaps in association with the spread of VAs and their resistance due to manure application in agricultural fields are also outlined. Finally, we highlight the areas that future research should prioritize and propose certain strategies that could help curtail VAs occurrence and the danger they pose to agro-ecosystems.