• baiting campaign;
  • iophenoxic acid;
  • marker;
  • vaccination;
  • wildlife


  1. Bait delivery of vaccines, toxicants or contraceptives to target wild mammals is an essential component of management strategies worldwide. Marking agents are required to enable the identification of individuals that consume the baits in order to evaluate and optimize the cost-efficacy of baiting campaigns.
  2. Ethyl-iophenoxic acid (Et-IPA) is an organic iodine-containing compound that has been used increasingly since the 1980s as a bait marker. It binds to proteins in animal blood and therefore can be detected indirectly by measuring plasma or serum iodine concentration or directly by measuring plasma or serum Et-IPA concentration with liquid chromatography. Methyl-iophenoxic acid and propyl-iophenoxic acid can also be used to provide quantitative information on temporal or spatial patterns of bait consumption in a range of mammalian species. We review the suitability of Et-IPA and its analogues as bait markers in mammals.
  3. The highly variable persistence of analogues and in species highlights the need for calibration testing of each compound as a marker for each species and for each proposed use before starting a bait delivery trial.
  4. After absorption, the fate of IPAs (by metabolism, distribution and excretion) is variable, but most are bound to plasma proteins. Marking efficacy is therefore high.
  5. The implications of exposure to IPAs for predators and humans were analyzed to evaluate its safety for delivery to wild mammals. Although it is highly unlikely that secondary exposure through ingestion could involve sufficiently large quantities to produce adverse effects, further studies are necessary to assess long-term effects after chronic exposure to these compounds.
  6. IPAs can mark animal serum for long periods of time, and improvements in detection methods for them are currently being developed, so that they are a good choice for oral baiting field experiments with mammals.