Effective dose and persistence of Rhodamine-B in wild pig Vibrissae
Due to substantial ecological and economic damage attributed to wild pigs (Sus scrofa), there is international interest in using pharmaceutical baits to control populations. To assess the efficacy and specificity of baiting programs, one may use chemical biomarkers to evaluate uptake of pharmaceutical baits. In particular, Rhodamine B (RB) is known to be an effective biomarker in wild pigs. However, significant data gaps exist regarding the minimum effective dosage and the persistence of RB in wild pigs. To investigate this we used a controlled double-blind study, administering a one-time dose of RB at three treatment levels (5, 15, or 30 mg/kg) to 15 pigs, with five pigs per treatment group. Facial vibrissae were collected pre-RB ingestion as a control and every 2 weeks post-RB ingestion for 12 weeks. We examined samples for RB presence and used a generalized linear mixed model (GLMM) to determine the influence of treatment dose on persistence of RB. Additionally, we measured distance moved by the RB mark away from the vibrissae root and used a GLMM to assess movement rates of RB bands along growing vibrissae. Here, we found consistently greater persistence of RB in the 15 and 30 mg/kg treatments across the sampling period (p = 0.005 and p = <0.0001, respectively). A significant, positive movement trend in RB bands was observed within the 15 and 30mg/kg groups. Based on our results, a 15 mg/kg dosage can be considered a minimum effective dose for wild pigs and will reliably produce a detectable RB mark up to and likely beyond 12 weeks post-ingestion.