Evaluation of the marking duration of iophenoxic acid (IPA) derivatives in raccoons ( Procyon lotor )

Abstract Biomarkers contribute to measuring uptake in wildlife baiting applications, such as oral rabies vaccination (ORV), when marking capabilities are adequately validated. One biomarker, iophenoxic acid (IPA), can exist in multiple analogues and has the potential of being a quantitative marker for ORV uptake, but the marking capabilities of the different analogues have not been adequately validated for target species, such as raccoons ( Procyon lotor ). We experimentally fed captive raccoons 4 different encapsulated IPA analogues, methyl, ethyl, butyl, and pentyl, at 3 different doses, 2.5 mg, 5 mg, and 10 mg, to evaluate marking and decay relative to dose. We then evaluated marking of 2 IPA analogues, ethyl and propyl, incorporated within the matrix of placebo ORV baits. We evaluated the concentration of each IPA analogue in raccoon serum using liquid chromatography tandem mass spectrometry. For marking and decay evaluation, all 4 IPAs at all doses marked raccoons beyond 454 days, and we observed dose‐dependent relationships with serum IPA concentration. Testing with ethyl or propyl in an ORV bait matrix at 1 mg IPA per bait marked raccoon sera for at least 67 days post‐consumption. All IPAs evaluated have use for estimating bait uptake by raccoons. The IPA analogue, sampling window, and dose are all factors to consider when selecting and using an IPA for estimating bait uptake in wildlife.