Patterns and Impacts of Antimicrobial Usage in Livestock

While very large quantities of antimicrobials are administered to food producing animals, usage in animal production is generally restricted to specific registered classes of antimicrobials and administration is generally for restricted periods of time in relatively isolated populations of animals. In contrast, antimicrobial usage in companion animals (dogs, cats and horses) is across a wider range of classes, within less isolated populations and in animals in near constant contact with humans. While some of this usage may not result in increased risk of transfer of resistance into humans, other patterns of prescribing may have a high risk, but there is little information available about the approaches to usage that pose the greatest risk. Any education of veterinary prescribers, or change in regulation of antimicrobial usage in veterinary practice, will depend on the acquisition of data to differentiate high-risk behaviour from that posing much lower risks. The data currently available about veterinary usage of antibiotics, as reported by the Australian Pesticides and Veterinary Medicines Authority (APVMA), is limited to the total tonnages of antimicrobials imported for veterinary purposes, with no differentiation of the distribution of these drugs to different animal species or production systems, and no information about the stage the animals’ lives when the drugs are administered. Administration for a short period of time to neonates is likely to have much less impact on transfer of resistance into the human food chain than administration over an extended period of time to older animals closer to the time of harvest.

The aim of the proposed studies will be to gain a clear understanding of the volumes of antimicrobials administered to different food animals, the specific antimicrobials used in typical herds and flocks and the distribution of this usage over the lifetime of these animals. The indications that serve as signals to prescribers will be explored to identify those that are justifiable and those that are questionable, and to identify health problems that might be the focus of alternative solutions. In addition, the rationale for specific choices of drug will be assessed and compared to the evidence available to support this use. This will further assist in identifying gaps in evidence for different prescribing patterns that can be addressed to guide improved behaviour.

Patterns and Rationales for Antimicrobial Usage in Companion Animals

While there is greater microbiological monitoring of infectious disease in companion animals as compared to farm animals, and data available within veterinary diagnostic laboratories on resistance patterns in a number of important indicator species, including Staphylococcus aureus, Staphylococcus pseudintermedius and Escherichia coli, there are no data available about usage patterns or the rationale behind these usage patterns.

At the conclusion of this study we will have identified factors driving antimicrobial prescribing in companion animal practice and located points for future interventions, including, potentially, improved prescribing guidelines and suitable mechanisms to ensure their use, educational programs at continuing education courses and incorporation of responsible prescribing into veterinary hospital accreditation programs.

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